1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions...

147
1 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16

Transcript of 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions...

Page 1: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

1

copy 2009 BrooksCole - Cengage

More About Chemical Equilibria

Acid-Base amp Precipitation

Reactions Chapter 15 amp 16

2

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 15bull Define the Common Ion Effect (151)bull Define buffer and show how a buffer

controls pH of a solution (152 153)bull Identify and Evaluate titration curves

(154)bull Use of Indicators (155)

3

copy 2009 BrooksCole - Cengage

Stomach Acidity ampAcid-Base Reactions

4

copy 2009 BrooksCole - Cengage

Acid-Base Reactions

bull Strong acid + strong base HCl + NaOH bull Strong acid + weak base

HCl + NH3 bull Weak acid + strong base HOAc + NaOH bull Weak acid + weak base

HOAc + NH3

What is relative pH

before during amp

after reaction

Need to study

a) Common ion

effect and buffers

b) Titrations

5

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Here we are adding NH4+ an ion COMMON to the

equilibrium

Le Chatelier predicts that the equilibrium will shift to the left (1) right (2) no change (3)

The pH will go up (1) down (2) no change (3)

NH4+ is an acid

The Common Ion Effect

Section 151

6

copy 2009 BrooksCole - Cengage

Let us first calculate the pH of a 025 M NH3 solution

[NH3] [NH4+] [OH-]

initial 025 0 0change -x +x +xequilib 025 - x x x

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

pH of Aqueous NH3

7

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x2

025 - x

pH of Aqueous NH3

Assuming x is ltlt 025 we have

[OH-] = x = [Kb(025)]12 = 00021 M

This gives pOH = 267

and so pH = 1400 - 267

= 1133 for 025 M NH3

8

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initialchangeequilib

pH of NH3NH4+ Mixture

9

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initial 025 010 0change -x +x +xequilib 025 - x 010 + x x

pH of NH3NH4+ Mixture

10

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x(010 + x)

025 - x

pH of NH3NH4+ Mixture

Assuming x is very small

[OH-] = x = (025 010)(Kb) = 45 x 10-5 M

This gives pOH = 435 and pH = 965pH drops from 1133 to 965

on adding a common ion

11

copy 2009 BrooksCole - Cengage

Common Ion Effectbull The addition of a common ion in a base such as ammonia

limits the ionization of the base and the production of [OH-] (Le Chacirctelierrsquos Principle)

B(aq) + H2O(l) HB+(aq) + OH-(aq)bull For acid addition of conjugate base from salt limit

ionization of acid which limits [H3O+]

HA(aq) + H2O(l) A-(aq) + H3O+(aq)bull Doesnrsquot work if the conjugate base is from a strong acid

because the conjugate base is too weakbull In other words adding Cl- to above does not change the pH

because the Cl- comes from strong acid HCl which has a very large Ka

HCl + H2O H3O+ + Cl-

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 2: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

2

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 15bull Define the Common Ion Effect (151)bull Define buffer and show how a buffer

controls pH of a solution (152 153)bull Identify and Evaluate titration curves

(154)bull Use of Indicators (155)

3

copy 2009 BrooksCole - Cengage

Stomach Acidity ampAcid-Base Reactions

4

copy 2009 BrooksCole - Cengage

Acid-Base Reactions

bull Strong acid + strong base HCl + NaOH bull Strong acid + weak base

HCl + NH3 bull Weak acid + strong base HOAc + NaOH bull Weak acid + weak base

HOAc + NH3

What is relative pH

before during amp

after reaction

Need to study

a) Common ion

effect and buffers

b) Titrations

5

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Here we are adding NH4+ an ion COMMON to the

equilibrium

Le Chatelier predicts that the equilibrium will shift to the left (1) right (2) no change (3)

The pH will go up (1) down (2) no change (3)

NH4+ is an acid

The Common Ion Effect

Section 151

6

copy 2009 BrooksCole - Cengage

Let us first calculate the pH of a 025 M NH3 solution

[NH3] [NH4+] [OH-]

initial 025 0 0change -x +x +xequilib 025 - x x x

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

pH of Aqueous NH3

7

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x2

025 - x

pH of Aqueous NH3

Assuming x is ltlt 025 we have

[OH-] = x = [Kb(025)]12 = 00021 M

This gives pOH = 267

and so pH = 1400 - 267

= 1133 for 025 M NH3

8

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initialchangeequilib

pH of NH3NH4+ Mixture

9

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initial 025 010 0change -x +x +xequilib 025 - x 010 + x x

pH of NH3NH4+ Mixture

10

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x(010 + x)

025 - x

pH of NH3NH4+ Mixture

Assuming x is very small

[OH-] = x = (025 010)(Kb) = 45 x 10-5 M

This gives pOH = 435 and pH = 965pH drops from 1133 to 965

on adding a common ion

11

copy 2009 BrooksCole - Cengage

Common Ion Effectbull The addition of a common ion in a base such as ammonia

limits the ionization of the base and the production of [OH-] (Le Chacirctelierrsquos Principle)

B(aq) + H2O(l) HB+(aq) + OH-(aq)bull For acid addition of conjugate base from salt limit

ionization of acid which limits [H3O+]

HA(aq) + H2O(l) A-(aq) + H3O+(aq)bull Doesnrsquot work if the conjugate base is from a strong acid

because the conjugate base is too weakbull In other words adding Cl- to above does not change the pH

because the Cl- comes from strong acid HCl which has a very large Ka

HCl + H2O H3O+ + Cl-

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 3: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

3

copy 2009 BrooksCole - Cengage

Stomach Acidity ampAcid-Base Reactions

4

copy 2009 BrooksCole - Cengage

Acid-Base Reactions

bull Strong acid + strong base HCl + NaOH bull Strong acid + weak base

HCl + NH3 bull Weak acid + strong base HOAc + NaOH bull Weak acid + weak base

HOAc + NH3

What is relative pH

before during amp

after reaction

Need to study

a) Common ion

effect and buffers

b) Titrations

5

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Here we are adding NH4+ an ion COMMON to the

equilibrium

Le Chatelier predicts that the equilibrium will shift to the left (1) right (2) no change (3)

The pH will go up (1) down (2) no change (3)

NH4+ is an acid

The Common Ion Effect

Section 151

6

copy 2009 BrooksCole - Cengage

Let us first calculate the pH of a 025 M NH3 solution

[NH3] [NH4+] [OH-]

initial 025 0 0change -x +x +xequilib 025 - x x x

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

pH of Aqueous NH3

7

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x2

025 - x

pH of Aqueous NH3

Assuming x is ltlt 025 we have

[OH-] = x = [Kb(025)]12 = 00021 M

This gives pOH = 267

and so pH = 1400 - 267

= 1133 for 025 M NH3

8

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initialchangeequilib

pH of NH3NH4+ Mixture

9

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initial 025 010 0change -x +x +xequilib 025 - x 010 + x x

pH of NH3NH4+ Mixture

10

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x(010 + x)

025 - x

pH of NH3NH4+ Mixture

Assuming x is very small

[OH-] = x = (025 010)(Kb) = 45 x 10-5 M

This gives pOH = 435 and pH = 965pH drops from 1133 to 965

on adding a common ion

11

copy 2009 BrooksCole - Cengage

Common Ion Effectbull The addition of a common ion in a base such as ammonia

limits the ionization of the base and the production of [OH-] (Le Chacirctelierrsquos Principle)

B(aq) + H2O(l) HB+(aq) + OH-(aq)bull For acid addition of conjugate base from salt limit

ionization of acid which limits [H3O+]

HA(aq) + H2O(l) A-(aq) + H3O+(aq)bull Doesnrsquot work if the conjugate base is from a strong acid

because the conjugate base is too weakbull In other words adding Cl- to above does not change the pH

because the Cl- comes from strong acid HCl which has a very large Ka

HCl + H2O H3O+ + Cl-

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 4: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

4

copy 2009 BrooksCole - Cengage

Acid-Base Reactions

bull Strong acid + strong base HCl + NaOH bull Strong acid + weak base

HCl + NH3 bull Weak acid + strong base HOAc + NaOH bull Weak acid + weak base

HOAc + NH3

What is relative pH

before during amp

after reaction

Need to study

a) Common ion

effect and buffers

b) Titrations

5

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Here we are adding NH4+ an ion COMMON to the

equilibrium

Le Chatelier predicts that the equilibrium will shift to the left (1) right (2) no change (3)

The pH will go up (1) down (2) no change (3)

NH4+ is an acid

The Common Ion Effect

Section 151

6

copy 2009 BrooksCole - Cengage

Let us first calculate the pH of a 025 M NH3 solution

[NH3] [NH4+] [OH-]

initial 025 0 0change -x +x +xequilib 025 - x x x

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

pH of Aqueous NH3

7

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x2

025 - x

pH of Aqueous NH3

Assuming x is ltlt 025 we have

[OH-] = x = [Kb(025)]12 = 00021 M

This gives pOH = 267

and so pH = 1400 - 267

= 1133 for 025 M NH3

8

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initialchangeequilib

pH of NH3NH4+ Mixture

9

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initial 025 010 0change -x +x +xequilib 025 - x 010 + x x

pH of NH3NH4+ Mixture

10

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x(010 + x)

025 - x

pH of NH3NH4+ Mixture

Assuming x is very small

[OH-] = x = (025 010)(Kb) = 45 x 10-5 M

This gives pOH = 435 and pH = 965pH drops from 1133 to 965

on adding a common ion

11

copy 2009 BrooksCole - Cengage

Common Ion Effectbull The addition of a common ion in a base such as ammonia

limits the ionization of the base and the production of [OH-] (Le Chacirctelierrsquos Principle)

B(aq) + H2O(l) HB+(aq) + OH-(aq)bull For acid addition of conjugate base from salt limit

ionization of acid which limits [H3O+]

HA(aq) + H2O(l) A-(aq) + H3O+(aq)bull Doesnrsquot work if the conjugate base is from a strong acid

because the conjugate base is too weakbull In other words adding Cl- to above does not change the pH

because the Cl- comes from strong acid HCl which has a very large Ka

HCl + H2O H3O+ + Cl-

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 5: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

5

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Here we are adding NH4+ an ion COMMON to the

equilibrium

Le Chatelier predicts that the equilibrium will shift to the left (1) right (2) no change (3)

The pH will go up (1) down (2) no change (3)

NH4+ is an acid

The Common Ion Effect

Section 151

6

copy 2009 BrooksCole - Cengage

Let us first calculate the pH of a 025 M NH3 solution

[NH3] [NH4+] [OH-]

initial 025 0 0change -x +x +xequilib 025 - x x x

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

pH of Aqueous NH3

7

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x2

025 - x

pH of Aqueous NH3

Assuming x is ltlt 025 we have

[OH-] = x = [Kb(025)]12 = 00021 M

This gives pOH = 267

and so pH = 1400 - 267

= 1133 for 025 M NH3

8

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initialchangeequilib

pH of NH3NH4+ Mixture

9

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initial 025 010 0change -x +x +xequilib 025 - x 010 + x x

pH of NH3NH4+ Mixture

10

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x(010 + x)

025 - x

pH of NH3NH4+ Mixture

Assuming x is very small

[OH-] = x = (025 010)(Kb) = 45 x 10-5 M

This gives pOH = 435 and pH = 965pH drops from 1133 to 965

on adding a common ion

11

copy 2009 BrooksCole - Cengage

Common Ion Effectbull The addition of a common ion in a base such as ammonia

limits the ionization of the base and the production of [OH-] (Le Chacirctelierrsquos Principle)

B(aq) + H2O(l) HB+(aq) + OH-(aq)bull For acid addition of conjugate base from salt limit

ionization of acid which limits [H3O+]

HA(aq) + H2O(l) A-(aq) + H3O+(aq)bull Doesnrsquot work if the conjugate base is from a strong acid

because the conjugate base is too weakbull In other words adding Cl- to above does not change the pH

because the Cl- comes from strong acid HCl which has a very large Ka

HCl + H2O H3O+ + Cl-

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 6: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

6

copy 2009 BrooksCole - Cengage

Let us first calculate the pH of a 025 M NH3 solution

[NH3] [NH4+] [OH-]

initial 025 0 0change -x +x +xequilib 025 - x x x

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

pH of Aqueous NH3

7

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x2

025 - x

pH of Aqueous NH3

Assuming x is ltlt 025 we have

[OH-] = x = [Kb(025)]12 = 00021 M

This gives pOH = 267

and so pH = 1400 - 267

= 1133 for 025 M NH3

8

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initialchangeequilib

pH of NH3NH4+ Mixture

9

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initial 025 010 0change -x +x +xequilib 025 - x 010 + x x

pH of NH3NH4+ Mixture

10

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x(010 + x)

025 - x

pH of NH3NH4+ Mixture

Assuming x is very small

[OH-] = x = (025 010)(Kb) = 45 x 10-5 M

This gives pOH = 435 and pH = 965pH drops from 1133 to 965

on adding a common ion

11

copy 2009 BrooksCole - Cengage

Common Ion Effectbull The addition of a common ion in a base such as ammonia

limits the ionization of the base and the production of [OH-] (Le Chacirctelierrsquos Principle)

B(aq) + H2O(l) HB+(aq) + OH-(aq)bull For acid addition of conjugate base from salt limit

ionization of acid which limits [H3O+]

HA(aq) + H2O(l) A-(aq) + H3O+(aq)bull Doesnrsquot work if the conjugate base is from a strong acid

because the conjugate base is too weakbull In other words adding Cl- to above does not change the pH

because the Cl- comes from strong acid HCl which has a very large Ka

HCl + H2O H3O+ + Cl-

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 7: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

7

copy 2009 BrooksCole - Cengage

QUESTION What is the effect on the pH of adding NH4Cl to 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x2

025 - x

pH of Aqueous NH3

Assuming x is ltlt 025 we have

[OH-] = x = [Kb(025)]12 = 00021 M

This gives pOH = 267

and so pH = 1400 - 267

= 1133 for 025 M NH3

8

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initialchangeequilib

pH of NH3NH4+ Mixture

9

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initial 025 010 0change -x +x +xequilib 025 - x 010 + x x

pH of NH3NH4+ Mixture

10

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x(010 + x)

025 - x

pH of NH3NH4+ Mixture

Assuming x is very small

[OH-] = x = (025 010)(Kb) = 45 x 10-5 M

This gives pOH = 435 and pH = 965pH drops from 1133 to 965

on adding a common ion

11

copy 2009 BrooksCole - Cengage

Common Ion Effectbull The addition of a common ion in a base such as ammonia

limits the ionization of the base and the production of [OH-] (Le Chacirctelierrsquos Principle)

B(aq) + H2O(l) HB+(aq) + OH-(aq)bull For acid addition of conjugate base from salt limit

ionization of acid which limits [H3O+]

HA(aq) + H2O(l) A-(aq) + H3O+(aq)bull Doesnrsquot work if the conjugate base is from a strong acid

because the conjugate base is too weakbull In other words adding Cl- to above does not change the pH

because the Cl- comes from strong acid HCl which has a very large Ka

HCl + H2O H3O+ + Cl-

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 8: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

8

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initialchangeequilib

pH of NH3NH4+ Mixture

9

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initial 025 010 0change -x +x +xequilib 025 - x 010 + x x

pH of NH3NH4+ Mixture

10

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x(010 + x)

025 - x

pH of NH3NH4+ Mixture

Assuming x is very small

[OH-] = x = (025 010)(Kb) = 45 x 10-5 M

This gives pOH = 435 and pH = 965pH drops from 1133 to 965

on adding a common ion

11

copy 2009 BrooksCole - Cengage

Common Ion Effectbull The addition of a common ion in a base such as ammonia

limits the ionization of the base and the production of [OH-] (Le Chacirctelierrsquos Principle)

B(aq) + H2O(l) HB+(aq) + OH-(aq)bull For acid addition of conjugate base from salt limit

ionization of acid which limits [H3O+]

HA(aq) + H2O(l) A-(aq) + H3O+(aq)bull Doesnrsquot work if the conjugate base is from a strong acid

because the conjugate base is too weakbull In other words adding Cl- to above does not change the pH

because the Cl- comes from strong acid HCl which has a very large Ka

HCl + H2O H3O+ + Cl-

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 9: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

9

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

We expect that the pH will decline on adding NH4Cl Letrsquos test that

[NH3] [NH4+] [OH-]

initial 025 010 0change -x +x +xequilib 025 - x 010 + x x

pH of NH3NH4+ Mixture

10

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x(010 + x)

025 - x

pH of NH3NH4+ Mixture

Assuming x is very small

[OH-] = x = (025 010)(Kb) = 45 x 10-5 M

This gives pOH = 435 and pH = 965pH drops from 1133 to 965

on adding a common ion

11

copy 2009 BrooksCole - Cengage

Common Ion Effectbull The addition of a common ion in a base such as ammonia

limits the ionization of the base and the production of [OH-] (Le Chacirctelierrsquos Principle)

B(aq) + H2O(l) HB+(aq) + OH-(aq)bull For acid addition of conjugate base from salt limit

ionization of acid which limits [H3O+]

HA(aq) + H2O(l) A-(aq) + H3O+(aq)bull Doesnrsquot work if the conjugate base is from a strong acid

because the conjugate base is too weakbull In other words adding Cl- to above does not change the pH

because the Cl- comes from strong acid HCl which has a very large Ka

HCl + H2O H3O+ + Cl-

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 10: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

10

copy 2009 BrooksCole - Cengage

Problem What is the pH of a solution with 010 M NH4Cl and 025 M NH3(aq)

NH3(aq) + H2O NH4+(aq) + OH-(aq)

Kb= 18 x 10-5 = [NH4

+ ][OH- ]

[NH3 ] =

x(010 + x)

025 - x

pH of NH3NH4+ Mixture

Assuming x is very small

[OH-] = x = (025 010)(Kb) = 45 x 10-5 M

This gives pOH = 435 and pH = 965pH drops from 1133 to 965

on adding a common ion

11

copy 2009 BrooksCole - Cengage

Common Ion Effectbull The addition of a common ion in a base such as ammonia

limits the ionization of the base and the production of [OH-] (Le Chacirctelierrsquos Principle)

B(aq) + H2O(l) HB+(aq) + OH-(aq)bull For acid addition of conjugate base from salt limit

ionization of acid which limits [H3O+]

HA(aq) + H2O(l) A-(aq) + H3O+(aq)bull Doesnrsquot work if the conjugate base is from a strong acid

because the conjugate base is too weakbull In other words adding Cl- to above does not change the pH

because the Cl- comes from strong acid HCl which has a very large Ka

HCl + H2O H3O+ + Cl-

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 11: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

11

copy 2009 BrooksCole - Cengage

Common Ion Effectbull The addition of a common ion in a base such as ammonia

limits the ionization of the base and the production of [OH-] (Le Chacirctelierrsquos Principle)

B(aq) + H2O(l) HB+(aq) + OH-(aq)bull For acid addition of conjugate base from salt limit

ionization of acid which limits [H3O+]

HA(aq) + H2O(l) A-(aq) + H3O+(aq)bull Doesnrsquot work if the conjugate base is from a strong acid

because the conjugate base is too weakbull In other words adding Cl- to above does not change the pH

because the Cl- comes from strong acid HCl which has a very large Ka

HCl + H2O H3O+ + Cl-

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 12: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

12

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 13: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

13

copy 2009 BrooksCole - Cengage

Common Ion Effect Practice

Calculate the pH of 030 M formic acid (HCO2H) in water and with enough sodium formate NaHCO2 to make the solution 010 M in the salt The Ka of formic acid is 18x10-4

HCO2H(aq) + H2O(l) HCO2-(aq) + H3O+

With salt

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 14: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

14

copy 2009 BrooksCole - Cengage

Buffered SolutionsSection 152

HCl is added to pure water

HCl is added to a solution of a weak acid H2PO4

- and its conjugate base HPO4

2-

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 15: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

15

copy 2009 BrooksCole - Cengage

A buffer solution is a special case of the common ion effect

The function of a buffer is to resist changes in the pH of a solution either by H+ or by OH-

Buffer CompositionWeak Acid + Conj BaseHOAc + OAc-

H2PO4- + HPO4

2-

NH4+

+ NH3

Buffer Solutions

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 16: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

16

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers workACID USES UP ADDED OH-

We know that

OAc- + H2O HOAc + OH-

has Kb = 56 x 10-10

Therefore the reverse reaction of the WEAK ACID with added OH-

has Kreverse = 1 Kb = 18 x 109

Kreverse is VERY LARGE so HOAc completely consumes OH-

Buffer Solutions

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 17: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

17

copy 2009 BrooksCole - Cengage

Consider HOAcOAc- to see how buffers work

CONJ BASE USES UP ADDED H+

HOAc + H2O OAc- + H3O+

has Ka = 18 x 10-5

Therefore the reverse reaction of the WEAK BASE with added H+

has Kreverse = 1 Ka = 56 x 104

Kreverse is VERY LARGE so OAc- completely consumes H3O+

Buffer Solutions

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 18: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

18

copy 2009 BrooksCole - Cengage

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

0700 M HOAc has pH = 245

The pH of the buffer will have

1 pH lt 245

2 pH gt 245

3 pH = 245

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 19: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

19

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

initialchangeequilib

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

0700 0600 0-x +x +x

0700 - x 0600 + x x

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 20: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

20

copy 2009 BrooksCole - Cengage

[HOAc] [OAc-] [H3O+]

equilib 0700 - x 0600 + x xAssuming that x ltlt 0700 and 0600 we have

Ka= 18 x 10-5 =

[H3O+ ](0600)

0700

Problem What is the pH of a buffer that has [HOAc] = 0700 M and [OAc-] = 0600 M

HOAc + H2O OAc- + H3O+

Ka = 18 x 10-5

Buffer Solutions

[H3O+] = 21 x 10-5 and pH = 468

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 21: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

21

copy 2009 BrooksCole - Cengage

Notice that the expression for calculating the H+ conc of the buffer is

[H3O+ ] = Orig conc of HOAc

Orig conc of OAc- x Ka

Buffer Solutions

Notice that the [H3O+] depends on

1the Ka of the acid2the ratio of the [acid] and

[conjugate base]

[H3O+ ] =

[Acid]

[Conj base] x Ka

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 22: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

22

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch Equation

Take the negative log of both sides of this equation

The pH is determined largely by the pKa of the acid and then adjusted by the ratio of conjugate base and acid

or

Note HA and A- are generic terms for acid and conjugate base respectively

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 23: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

23

copy 2009 BrooksCole - Cengage

Henderson-Hasselbalch EquationWorks the same for base

B(aq) + H2O(l) HB+(aq) + OH-(aq)

Solve for [OH-] =

Take the negative log of both sides of this equation to get

The pOH (and pH) is determined largely by the pKb of the base and then adjusted by the ratio of the conjugate acid and base

119901119874119867=119901119870 b+119949119952119944 iquestiquest

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 24: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

24

copy 2009 BrooksCole - Cengage

Buffer Calculation Example(AcidConj Base)

What is the pH of a buffer that is 012 M in lactic acid HC3H5O3 and 010 M in sodium lactate (NaC3H5O3)

Ka for lactic acid is 14 10-4

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 25: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

25

copy 2009 BrooksCole - Cengage

Buffer Calculation Example

HC3H5O3 + H2O C3H5O3- + H3O+

I 012 M 010 - E 012-x 010 + x x

x(010 + x) = 14x10-4

012 - xWersquoll make usual assumption that x is small

x = 012(140 x 10-4) = 168 x 10-4 = [H3O+]

010 So the pH = 377

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 26: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

26

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pH = ndashlog (14 10-4) + log(010)(012)

pH = 385 + (ndash008)

pH = 377 (same as before)

HC3H5O3 + H2O C3H5O3- + H3O+

acid conj base 012 010

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 27: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

27

copy 2009 BrooksCole - Cengage

Buffer Calculation using the HendersonndashHasselbalch Equation

pOH = ndashlog (18 x 10-5) + log(0045)(0080)

Calculate the pH of a buffer that has is 0080 M ammonia and 0045 M ammonium chlorideThe Kb for ammonia is 18 x 10-5 NH3(aq) + H2O(l) NH4

+(aq) + OH-(aq) [base] [conj acid] 0080 0045

pOH = 474 + (ndash025)pOH = 449pH = 1400 ndash 449 = 951

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 28: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

28

copy 2009 BrooksCole - Cengage

Buffer Practice 1

Calculate the pH of a solution that is 050 M HC2H3O2 (acetic acid) and 025 M NaC2H3O2

(Ka = 18 x 10-5) Use H-H Eqn

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 29: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

29

copy 2009 BrooksCole - Cengage

Buffer Practice 2Calculate the concentration of sodium benzoate (NaC7H5O2) that must be present in a 020 M solution of benzoic acid (HC7H5O2) to produce a pH of 400

(Benzoic acid Ka = 63 x 10-5)

Use Henderson-Hasselbalch equation

HC7H5O2 + H2O H3O+ + C7H5O2-

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 30: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

30

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

(How a Buffer Maintains pH)Problem What is the pH when 100 mL of 100 M HCl

is added toa) 100 L of pure water (before HCl pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [HCl] after adding 100 mL of HCl to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 999 x 10-4 M = [H3O+]

pH = 300

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 31: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

31

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

To play movie you must be in Slide Show Mode

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 32: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

32

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometry

H3O+ (from HCl) + OAc- (from buffer) rarr HOAc (from buffer)

The reaction occurs completely because K is very large

The stronger acid (H3O+) will react with the conj base of the weak acid (OAc-) to make the weak acid (HOAc)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (after HCl pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 33: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

33

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 1mdashStoichiometry

[H3O+] + [OAc-] [HOAc]

Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

000100 mol0600 mol 0700 mol

-000100 -000100 +000100

0 0599 mol 0701 mol

0 0599 mol1001 L

0701 mol 100l L

0598 molL0700 molL

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 34: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

34

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial (M)Change (M)Equil (M) (re-established)

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

0700 molL0 0598 molL-x +x +x

0598 + xx0700-x

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 35: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

35

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0700-x x 0598+x

Because [H3O+] = 21 x 10-5 M BEFORE adding HCl we again neglect x relative to 0700 and 0598

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 36: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

36

copy 2009 BrooksCole - Cengage

Adding an Acid to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 300)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468)

pH = 474 -007 = 467The pH has not changed muchon adding HCl to the buffer

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 37: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

37

copy 2009 BrooksCole - Cengage

Adding a Base to a BufferProblem What is the pH when 100 mL of 100 M

NaOH is added toa) 100 L of pure water (before NaOH pH = 700)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH = 468) (See slide 20)Solution to Part (a)Calc [OH-] after adding 100 mL of NaOH to 100 L of

water

M1bullV1 = M2 bull V2

(100 M)(10 mL) = M2(1001 mL)

M2 = 100 x 10-3 M = [OH-]

pOH = 300 pH = 1100

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 38: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

38

copy 2009 BrooksCole - Cengage

Adding an Base to a Buffer

Solution to Part (b)Step 1 mdash do the stoichiometryOH- (from NaOH) + HOAc (from buffer) rarr

OAc- (from buffer and rxn)The reaction occurs completely because K is

very largeThe strong base (OH-) will react with weak acid

(HOAc) to make the conj weak base (OAc-)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (after NaOH pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and

[OAc-] = 0600 M (pH before = 468)

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 39: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

39

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 1mdashStoichiometry [OH-] + [HOAc] rarr [OAc-]Before rxnChangeAfter rxnEquil []rsquos

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

000100 mol0700 mol 0600 mol

-000100 -000100 +000100

0 0699 mol 0601 mol0 0699 mol

1001 L0601 mol 1001 L

0698 molL0600 molL

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 40: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

40

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Initial(M)Change (M)Equil (M)(re-established)

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

0698 molL0 0600 molL-x +x +x

0600 + xx0698-x

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 41: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

41

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

[HOAc] [H3O+] [OAc-]

Equilibrium 0698-x x 0600+x

Because [H3O+] = 21 x 10-5 M BEFORE adding NaOH we again neglect x relative to 0600 and 0698

What is the pH when 100 mL of 100 M HCl is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468 pOH = 932)

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 42: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

42

copy 2009 BrooksCole - Cengage

Adding a Base to a Buffer

Solution to Part (b) Step 2mdashEquilibrium

HOAc + H2O H3O+ + OAc-

What is the pH when 100 mL of 100 M NaOH is added to a) 100 L of pure water (pH = 1100)b) 100 L of buffer that has [HOAc] = 0700 M and [OAc-]

= 0600 M (pH = 468)

pH = 474 ndash 007 = 467The pH has not changed muchon adding NaOH to the buffer

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 43: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

43

copy 2009 BrooksCole - Cengage

Preparing a BufferYou want to buffer a solution at pH = 430

This means [H3O+] = 10-pH =10-430= 50 x 10-5 M

It is best to choose an acid such that [H3O+] is about equal to Ka (or pH asymp pKa)

mdashthen you get the exact [H3O+] by adjusting the ratio of acid to conjugate base

[H3O+ ] =

[Acid]

[Conj base] x Ka

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 44: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

44

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

POSSIBLE

ACIDSCONJ BASE PAIRS Ka

HSO4- SO4

2- 12 x 10-2

HOAc OAc- 18 x 10-5

HCN CN- 40 x 10-10

Best choice is acetic acid acetate

Preparing a Buffer

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 45: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

45

copy 2009 BrooksCole - Cengage

You want to buffer a solution at pH = 430 or

[H3O+] = 50 x 10-5 M

[H3O+ ] = 50 x 10-5 = [HOAc]

[OAc- ] (18 x 10-5 )

Therefore if you use 0100 mol of NaOAc and 0278 mol of HOAc you will have pH = 430

Solve for [HOAc][OAc-] ratio =

278

1

Preparing a Buffer

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 46: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

46

copy 2009 BrooksCole - Cengage

A final point mdashCONCENTRATION of the acid and conjugate

base are not as important as the RATIO OF THE NUMBER OF MOLES of

each

Result diluting a buffer solution does not change its pH

Preparing a Buffer

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 47: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

47

copy 2009 BrooksCole - Cengage

Commercial Buffers

bull The solid acid and conjugate base in the packet are mixed with water to give the specified pH

bull Note that the quantity of water does not affect the pH of the buffer

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 48: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

48

copy 2009 BrooksCole - Cengage

Buffer prepared from

84 g NaHCO3 (84g84 gmol)

weak acid

160 g Na2CO3 (160106 gmol)

conjugate base

HCO3- + H2O

H3O+ + CO32-

What is the pH

HCO3- pKa = 103

pH = 103 + log (15110)=105

Preparing a Buffer

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 49: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

49

copy 2009 BrooksCole - Cengage

Buffer ExamplePhosphate buffers are used a lot in labs to simulate blood pH of 740 As with any other buffer you need an acid and its conjugate base

In this case the lsquoacidrsquo is NaH2PO4 and the lsquobasersquo is Na2HPO4 So the equilibrium expression is

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

A) If the pKa of H2PO4- is 721 what should the

[HPO42-][H2PO4

-] ratio be

B) If you weigh 60 g of NaH2PO4 and make 500 mL of solution how much Na2HPO4 do you need add to make your pH 740 buffer

(assume the Na2HPO4 doesnrsquot affect the volume)

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 50: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

50

copy 2009 BrooksCole - Cengage

Buffer ExamplePart A

H2PO4-(aq) + H2O(l) HPO4

2-(aq) + H3O+(aq)

Can use H-H pH = pKa + log[HPO42-][H2PO4

-]

740 = 721 + log[HPO42-][H2PO4

-]

log[HPO42-][H2PO4

-] = 019

[HPO42-][H2PO4

-] = 10019 = 155

Part B

60g NaH2PO4 = 0050 mol in 0500 L = 010 M

120gmol

[HPO42-] = 155[H2PO4

-] = 0155 M HPO42-

=0155 molL 0500 L 142 g Na2HPO4mol

= 110 g Na2HPO4

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 51: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

51

copy 2009 BrooksCole - Cengage

Preparing a buffer PracticeUsing the acetic acid (molar mass 60 gmol) and sodium acetate (molar mass 82 gmol) buffer from before how much sodium acetate should you weigh to make 10 L of a pH 500 buffer Assume [HOAc] is 10 M in the final 10 L of buffer (pKa = 474)

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 52: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

52

copy 2009 BrooksCole - Cengage

Buffering CapacityChapter 153

bull The pH of a buffered solution is

determined by the ratio [A-][HA]bull As long as the ratio doesnrsquot change much

the pH wonrsquot change much

bull The more concentrated these two are the

more H+ and OH- the solution will be able to absorb

bull Larger concentrations rarr bigger buffer capacity

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 53: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

53

copy 2009 BrooksCole - Cengage

Buffer Capacity

bull Calculate the change in pH that occurs when 0010 mol of HCl is added to 10L of each of the following

bull 500 M HOAc and 500 M NaOAcbull 0050 M HOAc and 0050 M NaOAc

bull Ka= 18x10-5 (pKa = 474)bull Note Since [OAc-]=[HOAc] for both cases

the initial pH is 474

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 54: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

54

copy 2009 BrooksCole - Cengage

Large Buffer System

H3O+ + OAc- HOAc + H2O

H3O+ OAc- HOAc

Before Reaction (moles) 001 500 500

After Reaction (moles) 0 499 501

Stoichiometry Calculation

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 55: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

55

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

0501 X 499 [base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 499501]

pH = 4738

Since pKa = 474 solution has gotten slightly more acidic

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 56: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

56

copy 2009 BrooksCole - Cengage

Small Buffer System

H3O+ + OAc- HOAc(aq) + H2O

H+ OAc- HOAc

Before Reaction (moles) 001 005 005

After Reaction (moles) 0 004 006

Stoichiometry Calculation

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 57: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

57

copy 2009 BrooksCole - Cengage

Calculating pH for Small Buffer System

In table form (Equilibrium Re-established)

[HOAc] M [H3O+] M [OAcminus] M

Initially 006 0 004

Change -x +x +x

At Equilibrium

006-x x 004 + x

HOAc H3O+ + OAc-

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 58: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

58

copy 2009 BrooksCole - Cengage

Calculate pH via Henderson-Hasselbalch Equations

At Equilibrium HOAc + H2O H3O+ + OAc-

006-x X 004-x

Ignore xrsquos relative to 006 and 004 since they will be small Calculate via H-H eqn

[base]pH = pKa +

[acid]

pH = -log (18 x 10-5) + log[ 004006]pH = 474 ndash 018 = 456

So solution is considerably more acidic than the pH 474 of the big buffer system

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 59: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

59

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Chapter 154

If you mix 500 mL of 010 M HCl and 500 mL of 010 NaOH what is the pHSince it is a strong acidstrong base what happens stoichiometrically

H+ + OH- H2O(l)

I(moles) 0005 0005 - After reaction 0 0 - Since you consume all acid and base and make water what is the pH 7 of course

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 60: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

60

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now what if you mix 500 mL of 010 M HCl and 200 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0002 - After reaction (mol) 0003 0 -Total volume of solution is 700 mL (00700 L)So the [H+] = 0003 mol00700 L = 00429 M pH = -log[00429] = 137

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 61: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

61

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)Now mix 500 mL of 010 M HCl and 700 mL of 010 NaOH what is the pH

H+ + OH- H2O(l)

I(moles) 0005 0007 - After reaction (mol) - 0002 -Total volume of solution is 1200 mL (01200 L)Since there was more OH- added than H+ all of the H+ is consumed and there is excess OH-[OH-] = 00020120 L = 0017 M OH-

pOH = 177 so pH = 1223

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 62: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

62

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 0005 0005 - After reaction 0 0 - 0005Since HOAc is a weak acid and OH- is a strong base the OH- will still consume (take that H+) from the HOAc (The Stoichiometry part)

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 63: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

63

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

Need Conc 0005 mol0100L I (conc) 005 0 0 C -x +x +x E 0050-x x xYou can think of this part as when we calculated pHrsquos of salts of weak acids It doesnrsquot matter how you get to this point the calculation is still the same

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 64: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

64

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 500 mL of 010 NaOH what is the pHNow equilibrium will be re-established

H2O(l) + OAc- HOAc + OH-

E 0050-x x x

Krxn =Kb = KwKa = 1x10-1418x10-5 = 556x10-10

= 556x10-10

Usual assumption that x is small compared to 0050 so x = pOH = -log[527x10-6] = 528 so pH = 872

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 65: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

65

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHSince it is a weak acidstrong base what happens stoichiometrically

HOAc + OH- H2O(l) + OAc-

I(moles) 00050 00020 0 Reaction -00020 -00020 +00020After reaction 00030 0 00020

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 66: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

66

copy 2009 BrooksCole - Cengage

Mixing Acids and Bases(Stoichiometry amp

Equilibrium)If you mix 500 mL of 010 M HOAc and 200 mL of 010 NaOH what is the pHNow equilibrium will be re-established Since you have an acid and its conjugate base this is a buffer and you can use H-H eqn

H2O(l) + HOAc OAc- + H3O+

E 00030 00020 x pH = pKa + log [OAc-][HOAc] = 474 + log(0002)(0003) = 474 + log(0667) = 474 ndash 018 = 456

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 67: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

67

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesTitrations and pH Curves

pHpH

Titrant volume mLTitrant volume mL

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 68: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

68

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Adding NaOH from the buret to acetic acid in the flask a weak acid In the beginning the pH increases very

slowly

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 69: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

69

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH rises as equivalence point is approached

>

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 70: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

70

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Additional NaOH is added pH increases and then levels off as NaOH is added beyond the equivalence

point

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 71: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

71

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

What is the pH at equivalence point

What is the pH at equivalence point

pH of solution of benzoic acid a weak acid

pH of solution of benzoic acid a weak acidBenzoic acid

+ NaOHBenzoic acid + NaOH

What is pH at half-way point

What is pH at half-way point

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 72: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

72

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

C6H5CO2H = HBz Benzoate ion = Bz-

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 73: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

73

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

The pH of the final solution will be1 Less than 72 Equal to 73 Greater than 7

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

HBz + NaOH Na+ + Bz- + H2O

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 74: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

74

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

The product of the titration of benzoic acid is the benzoate ion Bz-

Bz- is the conjugate base of a weak acid Therefore solution is basic at

equivalence point

Bz- + H2O HBz + OH-

Kb = 16 x 10-10

++

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 75: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

75

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point

pH at equivalence point is basic

pH at equivalence point is basic

Benzoic acid + NaOHBenzoic acid + NaOH

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 76: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

76

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Strategy mdash find the conc of the conjugate base Bz- in the solution AFTER the titration then calculate pH

This is a two-step problem1stoichiometry of acid-base reaction2equilibrium calculation

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 77: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

77

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION1 Calc moles of NaOH reqrsquod(0100 L HBz)(0025 M) = 00025 mol HBzThis requires 00025 mol NaOH2Calc volume of NaOH reqrsquod00025 mol (1 L 0100 mol) = 0025 L25 mL of NaOH reqrsquod

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 78: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

78

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

STOICHIOMETRY PORTION25 mL of NaOH reqrsquod 3 Moles of Bz- produced = moles HBz =

00025 mol4 Calc conc of Bz-

There are 00025 mol of Bz- in a TOTAL SOLUTION VOLUME of

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at the equivalence point

125 mL

[Bz-] = 00025 mol 0125 L = 0020 M

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 79: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

79

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate

ion Bz- the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

[Bz-] [HBz] [OH-]initial 0020 0 0change- x +x +x equilib 0020 - x x x

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 80: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

80

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

Equivalence PointMost important species in solution is benzoate ion Bz-

the weak conjugate base of benzoic acid HBz

Bz- + H2O HBz + OH- Kb = 16 x 10-10

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at equivalence point

x = [OH-] = 18 x 10-6

pOH = 575 and pH = 825

Kb = 16 x 10-10 =

x2

0020 - x

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 81: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

81

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point1 lt 72 = 73 gt 7

pH at half-way point1 lt 72 = 73 gt 7

Equivalence point pH = 825

Equivalence point pH = 825

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 82: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

82

copy 2009 BrooksCole - Cengage

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

QUESTION You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH to the equivalence point What is the pH at half-way point

pH at half-way point

pH at half-way point Equivalence point

pH = 825

Equivalence point pH = 825

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 83: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

83

copy 2009 BrooksCole - Cengage

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What is the pH at the half-way point

[H3O+ ] = [HBz]

[Bz- ] x Ka

At the half-way point [HBz] = [Bz-]Therefore [H3O+] = Ka = 63 x 10-5

pH = 420 = pKa of the acid

Both HBz and Bz- are present

This is a BUFFER

Both HBz and Bz- are present

This is a BUFFER

HBz + H2O H 3O+ + Bz- Ka = 63 x 10-5

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 84: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

84

copy 2009 BrooksCole - Cengage

Titrations and pH CurvesYou titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

What was the pH when 60 mL of NaOH was added

StoichiometryBefore rxn moles 00006 00025 --After rxn mole 0 00019 00006After rxn [ ] 0 00019mol0106L 000060106 0 0018 00057 Equilbrium HBz + H2O H3O+ + Bz- pKa = 420EquilibriumNow can use H-H equationpH = 420 + log (000570018) = 420 ndash 50 = 370Remember this is essentially a buffer solution since HBz and Bz- are both in the solution

When doing these types of problems start from initial moles and go to the point you are considering

OH- + HBz H2O + Bz-

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 85: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

85

copy 2009 BrooksCole - Cengage

OH- + HBz H2O + Bz-

Titrations and pH Curves

You titrate 100 mL of a 0025 M solution of benzoic acid with 0100 M NaOH

Practice What is the pH when 200 mL of NaOH are added

StoichiometryBefore rxn moles 00020 00025 --After rxn mole 0 00005 00020After rxn [ ] 0 00005mol0120L 000200120 0 00042 0017

Equilbrium HBz + H2O H2O + Bz- pKa = 420

EquilibriumNow can use H-H equationpH = 420 + log (001700042) = 420 + 061 = 481

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 86: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

86

copy 2009 BrooksCole - Cengage

Acetic acid titrated with NaOH

Weak acid titrated with a strong base

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 87: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

87

copy 2009 BrooksCole - Cengage

See Figure 184

Strong acid titrated with a strong base

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 88: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

88

copy 2009 BrooksCole - Cengage

Weak diprotic acid (H2C2O4) titrated with a strong base

(NaOH)

See Figure 186

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 89: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

89

copy 2009 BrooksCole - Cengage

Titration of a1 Strong acid with strong base2 Weak acid with strong base3 Strong base with weak acid4 Weak base with strong acid5 Weak base with weak acid6 Weak acid with weak base

pH

Volume of titrating reagent added --gt

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 90: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

90

copy 2009 BrooksCole - Cengage

Weak base (NH3) titrated with a strong

acid (HCl)

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 91: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

91

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsChapter 155

bull Weak acids that change color when they become bases

bull Since the Indicator is a weak acid it has a Ka

bull End point - when the indicator changes color

bull An indicator changes colors at pH=pKa1 pKa is the acid dissoc constant for the indicator

bull Want an indicator where pKa pH at equiv pt

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 92: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

92

copy 2009 BrooksCole - Cengage

Acid-Base IndicatorsAcid-Base Indicators

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 93: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

93

copy 2009 BrooksCole - Cengage

Indicators for Acid-Base Titrations

Indicators for Acid-Base Titrations

Since the pH change is large near the equivalence point you want an indicator that is one color before and one color after

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 94: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

94

copy 2009 BrooksCole - Cengage

Titration of a Base with an Acid

bull The pH at the equivalence point in these titrations is lt 7

bull Methyl red is the indicator of choice

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 95: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

95

copy 2009 BrooksCole - Cengage

Solubility and Complex Ion Equilibria

Chapter 16

Solubility and Complex Ion Equilibria

Chapter 16

Lead(II) iodide

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 96: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

96

copy 2009 BrooksCole - Cengage

Objectives ndash Chapter 16

bull Define equilibrium constant for lsquoinsolublersquo salts (Ksp) (161)

bull Manipulate solubility by common ion effect (161)

bull Precipitation Reactions ndash comparing Q amp K of a reaction (162)

bull Define Complex ion amp show how complex ions affect solubility (163)

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 97: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

97

copy 2009 BrooksCole - Cengage

Types of Chemical Reactions

bull EXCHANGE REACTIONS AB + CD AD + CB

ndash Acid-base CH3CO2H + NaOH NaCH3CO2 + H2O

ndash Gas forming CaCO3 + 2 HCl CaCl2 + CO2(g) + H2O

ndash Precipitation Pb(NO3) 2 + 2 KI PbI2(s) + 2 KNO3

bull OXIDATION REDUCTION (Redox ndash Ch 18)ndash 4 Fe + 3 O2 2 Fe2O3

bull Apply equilibrium principles to acid-base and precipitation reactions

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 98: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

98

copy 2009 BrooksCole - Cengage

Analysis of Silver Group

Analysis of Silver Group

All salts formed in this experiment are said to be INSOLUBLE and form when mixing moderately concentrated solutions of the metal ion with chloride ions

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 99: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

99

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAlthough all salts formed in this experiment are

said to be insoluble they do dissolve to some

SLIGHT extent

AgCl(s) Ag+(aq) + Cl-(aq)

When equilibrium has been established no more

AgCl dissolves and the solution is SATURATED

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 100: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

100

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

When solution is SATURATED expt shows that [Ag+] = 167 x 10-5 M

This is equivalent to the SOLUBILITY of AgCl

What is [Cl-]

[Cl-] = [Ag+] = 167 x 10-5 M

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 101: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

101

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

GroupAgCl(s) Ag+(aq) + Cl-(aq)

Saturated solution has

[Ag+] = [Cl-] = 167 x 10-5 M

Use this to calculate Kc

Kc = [Ag+] [Cl-]

= (167 x 10-5)(167 x 10-5)

= 279 x 10-10

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 102: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

102

copy 2009 BrooksCole - Cengage

Analysis of Silver

Group

Analysis of Silver

Group

AgCl(s) Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 279 x 10-10

Because this is the product of ldquosolubilitiesrdquo we call it

Ksp = solubility product

constant

bull See Table 161 and Appendix A54bull Note The property lsquosolubilityrsquo is in molL

(Can also be expressed as gL or mgL)bull Solubility Product has no units

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

Ag+ Pb2+ Hg22+

AgCl PbCl2 Hg2Cl2

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 103: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

103

copy 2009 BrooksCole - Cengage

Solubility ProductsIn general for the equilibrium for the reaction is expressed as

MmAa(s) mM+(aq) + aA-(aq)

The Ksp equilibrium expression is

Ksp =[M+]m[A-]a

The higher the Ksp the more soluble the salt is

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 104: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

104

copy 2009 BrooksCole - Cengage

Some Values of Ksp

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 105: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

105

copy 2009 BrooksCole - Cengage

Lead(II) ChloridePbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5 = [Pb2+][Clndash]2

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 106: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

106

copy 2009 BrooksCole - Cengage

Solution

1 Solubility = [Pb2+] = 130 x 10-3 M

[I-] =

[I-] = 2 x [Pb2+] = 260 x 10-3 M

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 107: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

107

copy 2009 BrooksCole - Cengage

Solution

2 Ksp = [Pb2+] [I-]2

= [Pb2+] 2 bull [Pb2+]2

Ksp = 4 [Pb2+]3

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

= 4 (solubility)3= 4 (solubility)3

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

Consider PbI2 dissolving in water

PbI2(s) Pb2+(aq) + 2 I-(aq)

Calculate Ksp

if solubility = 000130 M

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 108: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

108

copy 2009 BrooksCole - Cengage

Caveat

3 The value we just calculated by

solubility gives a ball-park value

The actual Ksp of PbI2 is 98 x 10-9

Note Calculating Ksp from solubility

gives approximate values that can be off by a few OOMs due to ionic interactions

Solubility of Lead(II) Iodide

Solubility of Lead(II) Iodide

Ksp = 4 (130 x 10-3)3 = 879 x 10-9Ksp = 4 (130 x 10-3)3 = 879 x 10-9

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 109: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

109

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 1bull Calculate the Ksp if the solubility of CaC2O4 is 61

mgL Note units here What should they be in order to determine Ksp (Molar Mass = 1281 gmol)

CaC2O4 (s) Ca2+(aq) + C2O42-(aq)

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 110: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

110

copy 2009 BrooksCole - Cengage

SolubilityKsp Practice 2bull Calculate the solubility of CaF2 in gL if the

Ksp is 39x10-11 (Molar Mass = 781 gmol)

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 111: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

111

copy 2009 BrooksCole - Cengage

The Common Ion EffectAdding an ion ldquocommonrdquo to an

equilibrium causes the equilibrium to shift back to reactant

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 112: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

112

copy 2009 BrooksCole - Cengage

Common Ion EffectPbCl2(s) Pb2+(aq) + 2 Cl-(aq)

Ksp = 19 x 10-5

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 113: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

113

copy 2009 BrooksCole - Cengage

Barium

Sulfate

Ksp = 11 x 10-10

(b) BaSO4 is opaque to x-rays Drinking a BaSO4 cocktail enables a physician to exam the intestines

(a) BaSO4 is a common mineral appearing a white powder or colorless crystals

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 114: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

114

copy 2009 BrooksCole - Cengage

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2

Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

Solution

Solubility in pure water = [Ba2+] = [SO42-] = x

Ksp = [Ba2+] [SO42-] = x2

x = (Ksp)12 = 11 x 10-5 M

Solubility in pure water = 11 x 10-5 molL

The Common Ion Effect

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 115: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

115

copy 2009 BrooksCole - Cengage

SolutionSolubility in pure water = 11 x 10-5 molL

Now dissolve BaSO4 in water already containing 0010 M Ba2+

Which way will the ldquocommon ionrdquo shift the equilibrium ___ Will solubility of BaSO4 be less than or greater than in pure water___

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 116: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

116

copy 2009 BrooksCole - Cengage

Solution

[Ba2+] [SO42-]

initialchange equilib

The Common Ion Effect

+ y0010 0

+ y

0010 + y y

Calculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 117: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

117

copy 2009 BrooksCole - Cengage

Solution

Ksp = [Ba2+] [SO42-] = (0010 + y) (y)

Because y lt 11 x 10-5 M (= x the solubility in pure water) this means 0010 + y is about equal to 0010 Therefore

Ksp = 11 x 10-10 = (0010)(y)

y = 11 x 10-8 M = solubility in presence of added Ba2+ ion

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 118: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

118

copy 2009 BrooksCole - Cengage

SUMMARYSolubility in pure water = x = 11 x 10-5 MSolubility in presence of added Ba2+

= 11 x 10-8 MLe Chatelierrsquos Principle is followed

The Common Ion EffectCalculate the solubility of BaSO4 in (a) pure water and (b) in 0010 M Ba(NO3)2Ksp for BaSO4 = 11 x 10-10

BaSO4(s) Ba2+(aq) + SO42-(aq)

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 119: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

119

copy 2009 BrooksCole - Cengage

Common Ion Effect PracticeDo you expect the solubility of AgI to be greater in pure water or in 0020 M AgNO3 Explain your answer

Ksp(AgI) = 85 x 10-17

AgI(s) Ag+(aq) + I-(aq)

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 120: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

120

copy 2009 BrooksCole - Cengage

Factors Affecting Solubility - pH

bull pHndash If a substance has a

basic anion (like OH-) it is more soluble in a more acidic solution

ndash Substances with acidic cations (Al3+) are more soluble in more basic solutions

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 121: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

121

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in water

Equilibrium Mg(OH)2 Mg2+ + 2OH-

For Ksp = 18 x 10-11 calculate pH

18 x 10-11 = x(2x)2

x = 165 x 10-4 M [solubility of Mg(OH)2]

= [Mg2+] in solution

[OH-] = 2 x solubility of Mg(OH)2

pOH = -log (2 middot 165 x 10-4) = 348pH = 1052

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 122: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

122

copy 2009 BrooksCole - Cengage

Solubility in more Acidic Solution example solid Mg(OH)2 in pH=9

bufferbull Now put Mg(OH)2 in a pH = 9 buffer solution bull Now [OH-] = 1 x 10-5 (if pH =9 then pOH = 5)bull [Mg2+][OH-]2 = 18 x 10-11 (Ksp a function of Temp

only)bull [Mg2+] = 18x10-11(1x10-5)2 = 018 Mbull Considerably more soluble (~1000x) in more

acidic solutionbull Solubility in water was 165 x 10-4 Mbull Essentially removed OH- by reacting with H+

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 123: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

123

copy 2009 BrooksCole - Cengage

Acidic solution example Ag3PO4

bull Ag3(PO4) is more soluble in acid solution than neutral solution Why

ndash H+ of acid solution reacts with PO43- anion to

produce weak acid HPO42-

Ag3PO4(s) 3Ag+(aq) + PO43-(aq) Ksp = 18x10-18

H+(aq) + PO43- (aq) HPO4

2-(aq) K = 1Ka = 28x1012

Ag3PO4(s) + H+ 3Ag+(aq) + HPO42(aq) K = 50 x 10-6

ndash Addition of H+ shifts equilibrium of 1st rxn to right

ndash PO43- is actually a moderately strong base

PO43- + H2O HPO4

2- + OH- Kb3 = 28x10-2

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 124: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

124

copy 2009 BrooksCole - Cengage

Acidic solution example AgClbull What about AgCl in an acidic solution such

as HNO3 or H2SO4AgCl(s) Ag+(aq) + Cl-(aq) Ksp = 18x10-10

H+(aq) + Cl- (aq)larr HCl(aq) K = very small

bull K of reaction remains very small largely determined by the Ksp of AgCl

bull Note Special case of HCl bull HCl will affect solubility How Whybull It would add chloride actually make AgCl less

soluble by Le Chatelier

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 125: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

125

copy 2009 BrooksCole - Cengage

Solubility and Aciditybull Other conjugate base anions that will increase in

solubility in an acidic solution

OH- F- S2- CO32- C2O4

2- and CrO42-

Why Because all form weak acids

Examples

PbS(s) + 2H+(aq) H2S(g) + Pb2+(aq)

Ca(OH)2(s) + 2H+(aq) 2H2O(l) + Ca2+(aq)

BaCO3(s) + 2H+(aq) CO2(g) + H2O(l) + Ba2+(aq)

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 126: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

126

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative AnalysisSection 162

Precipitation and Qualitative AnalysisSection 162

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

If [Hg22+] = 0010 M what [Cl-] is reqrsquod to just

begin the precipitation of Hg2Cl2

That is what is the maximum [Cl-] that can be

in solution with 0010 M Hg22+ without

forming Hg2Cl2

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 127: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

127

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Recognize that

Ksp = product of maximum ion concs

Precip begins when product of

ion concentrations (Q)

EXCEEDS the Ksp

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 128: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

128

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18 = [Hg22+] [Cl-]2

Solution

[Cl-] that can exist when [Hg22+] = 0010 M

[Cl- ] =

Ksp

0010 = 11 x 10-8 M

If this conc of Cl- is just exceeded Hg2Cl2 begins to precipitate

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 129: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

129

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysis

Hg2Cl2(s) Hg22+(aq) + 2 Cl-(aq)

Ksp = 11 x 10-18

Now raise [Cl-] to 10 M What is the value of [Hg2

2+] at this point

Solution

[Hg22+] = Ksp [Cl-]2

= Ksp (10)2 = 11 x 10-18 M

The concentration of Hg22+ has been reduced

by 1016

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 130: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

130

copy 2009 BrooksCole - Cengage

Precipitation and Qualitative Analysisndash Practice

bull If a solution is 0020 M in Cl- ions at what concentration of Pb2+ does the PbCl2 (Ksp= 17 x 10-5) precipitate

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 131: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

131

copy 2009 BrooksCole - Cengage

Separating Metal Ions Cu2+ Ag+ Pb2+

Separating Metal Ions Cu2+ Ag+ Pb2+

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

Ksp Values

AgCl 18 x 10-10

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 132: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

132

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

Separating Salts by Differences in Ksp

bull Add CrO42- to solid PbCl2 The less

soluble salt PbCrO4 precipitates

bull PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

bull Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 133: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

133

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

PbCl2(s) + CrO42- PbCrO4 + 2 Cl-

Salt Ksp

PbCl2 17 x 10-5

PbCrO4 18 x 10-14

PbCl2(s) Pb2+ + 2 Cl- K1 = Ksp

Pb2+ + CrO42- PbCrO4 K2 = 1Ksp

Knet = (K1)(K2) = 94 x 108

Net reaction is product-favored

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 134: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

134

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in Ksp

The color of the salt silver chromate Ag2CrO4 is red A student adds a solution of Pb(NO3)2 to a test tube containing solid red Ag2CrO4 After stirring the contents of the test tube the student finds the contents changes from red to yellowWhat is the yellow salt Which one has a higher Ksp

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 135: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

135

copy 2009 BrooksCole - Cengage

Separating Salts by Differences in KspSolution

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 136: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

136

copy 2009 BrooksCole - Cengage

Separations by Difference in Ksp

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 137: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

137

copy 2009 BrooksCole - Cengage

Qualitative AnalysisFigure 162Group 1 ndash Insoluble ChloridesGroup 2 ndash Sulfides Insoluble in acidGroup 3 ndash Sulfides insoluble in baseGroup 4 ndash Insoluble CarbonatesGroup 5 ndash Alkali Metal and ammonium ions

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 138: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

138

copy 2009 BrooksCole - Cengage

The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3 leads to COMPLEX

IONS

Equilibria Involving Complex Ions

Chapter 163

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 139: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

139

copy 2009 BrooksCole - Cengage

Reaction of NH3 with Cu2+

(aq)

>

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 140: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

140

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull Consider the formation of Ag(NH3)2

+

Ag+(aq) + 2NH3(aq) Ag(NH3)2+(aq)

bull The Ag(NH3)2+ is called a complex ion

bull A Complex Ion is a central transition metal ion that is bonded to a group of surrounding molecules or ions and carries a net charge It happens a lot with transition metals because they have available d-orbitals Bases like ammonia are attracted to that

(See Chapter 21 for details)

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 141: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

141

copy 2009 BrooksCole - Cengage

Solubility and Complex Ionsbull

bull Note that the equilibrium expression is lsquooppositersquo to what we usually write the individual species are on the left and the new substance on the right This leads to Kfrsquos that are very LARGE

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 142: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

142

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 143: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

143

copy 2009 BrooksCole - Cengage

Formation of complex ions explains why you can dissolve a ppt by forming a complex ion

Dissolving Precipitates by forming Complex Ions

AgCl(s) + 2 NH3 Ag(NH3)2+ + Cl-

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 144: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

144

copy 2009 BrooksCole - Cengage

Solubility and Complex Ions

bull Complex Ionsndash The formation

of these complex ions increase the solubility of these salts

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 145: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

145

copy 2009 BrooksCole - Cengage

Determine the Keq of a reaction if the solution contains AgBr and NH3bull In water solid AgBr exists in equilibrium with its

ions according to

AgBr Ag+ + Br- Ksp = 5 x 10-13

bull Also Ag+ make complex ions with ammonia

expressed as

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

Solubility and Complex Ions Example

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 146: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

146

copy 2009 BrooksCole - Cengage

bull Therefore the equilibrium expressed by both reactions is

AgBr Ag+ + Br- Ksp = 5 x 10-13

Ag+ + 2NH3 Ag(NH3)2+ Kf = 17 x 107

AgBr + 2NH3 Ag(NH3)2+ + Br- Keq = 85 x 10-6

Keq = Ksp x Kf

bull So this shows overall that the equilibrium is more to the right (aqueous ions) than the dissolution of the AgBr itself in pure water

bull In other words NH3 makes AgBr more soluble

Solubility and Complex Ions Example

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice
Page 147: 1 © 2009 Brooks/Cole - Cengage More About Chemical Equilibria Acid-Base & Precipitation Reactions Chapter 15 & 16.

147

copy 2009 BrooksCole - Cengage

AP Exam PracticeKsp Problemsbull 2011B AP Exam 1bull 2010 AP Exam 1bull 2006 AP Exam 1bull 2004 AP Exam 1bull 2001 AP Exam 1

Complex AB Problemsbull 2011 AP Exam 1bull 2006B AP Exam 1bull 2003 AP Exam 1bull 2002B AP Exam 1bull 2002 AP Exam 1

  • More About Chemical Equilibria Acid-Base amp Precipitation React
  • Objectives ndash Chapter 15
  • Stomach Acidity amp Acid-Base Reactions
  • Acid-Base Reactions
  • The Common Ion Effect Section 151
  • Slide 6
  • Slide 7
  • Slide 8
  • pH of NH3NH4+ Mixture
  • pH of NH3NH4+ Mixture (2)
  • Common Ion Effect
  • Common Ion Effect Practice
  • Common Ion Effect Practice (2)
  • Buffered Solutions Section 152
  • Buffer Solutions
  • Buffer Solutions (2)
  • Buffer Solutions (3)
  • Buffer Solutions (4)
  • Buffer Solutions (5)
  • Buffer Solutions (6)
  • Buffer Solutions (7)
  • Henderson-Hasselbalch Equation
  • Henderson-Hasselbalch Equation (2)
  • Buffer Calculation Example (AcidConj Base)
  • Buffer Calculation Example
  • Buffer Calculation using the HendersonndashHasselbalch Equation
  • Buffer Calculation using the HendersonndashHasselbalch Equation (2)
  • Buffer Practice 1
  • Buffer Practice 2
  • Adding an Acid to a Buffer (How a Buffer Maintains pH)
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer
  • Adding an Acid to a Buffer (2)
  • Adding an Acid to a Buffer (3)
  • Adding an Acid to a Buffer (4)
  • Adding an Acid to a Buffer (5)
  • Adding a Base to a Buffer
  • Adding an Base to a Buffer
  • Adding a Base to a Buffer (2)
  • Adding a Base to a Buffer (3)
  • Adding a Base to a Buffer (4)
  • Adding a Base to a Buffer (5)
  • Preparing a Buffer
  • Preparing a Buffer (2)
  • Preparing a Buffer (3)
  • Preparing a Buffer (4)
  • Commercial Buffers
  • Preparing a Buffer (5)
  • Buffer Example
  • Buffer Example (2)
  • Preparing a buffer Practice
  • Buffering Capacity Chapter 153
  • Buffer Capacity
  • Large Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations
  • Small Buffer System
  • Calculating pH for Small Buffer System
  • Calculate pH via Henderson-Hasselbalch Equations (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) Chapter 15
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (2)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (3)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (4)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (5)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (6)
  • Mixing Acids and Bases (Stoichiometry amp Equilibrium) (7)
  • Slide 67
  • Titrations and pH Curves
  • Titrations and pH Curves (2)
  • Titrations and pH Curves (3)
  • Slide 71
  • Titrations and pH Curves (4)
  • Titrations and pH Curves (5)
  • Titrations and pH Curves (6)
  • Slide 75
  • Titrations and pH Curves (7)
  • Titrations and pH Curves (8)
  • Titrations and pH Curves (9)
  • Titrations and pH Curves (10)
  • Titrations and pH Curves (11)
  • Slide 81
  • Slide 82
  • Titrations and pH Curves (12)
  • Titrations and pH Curves (13)
  • Titrations and pH Curves (14)
  • Acetic acid titrated with NaOH
  • Strong acid titrated with a strong base
  • Weak diprotic acid (H2C2O4) titrated with a strong base (NaOH)
  • Slide 89
  • Weak base (NH3) titrated with a strong acid (HCl)
  • Acid-Base Indicators Chapter 155
  • Acid-Base Indicators
  • Indicators for Acid-Base Titrations
  • Titration of a Base with an Acid
  • Solubility and Complex Ion Equilibria Chapter 16
  • Objectives ndash Chapter 16
  • Types of Chemical Reactions
  • Analysis of Silver Group
  • Analysis of Silver Group (2)
  • Analysis of Silver Group (3)
  • Analysis of Silver Group (4)
  • Analysis of Silver Group (5)
  • Solubility Products
  • Slide 104
  • Lead(II) Chloride
  • Solubility of Lead(II) Iodide
  • Solubility of Lead(II) Iodide (2)
  • Solubility of Lead(II) Iodide (3)
  • SolubilityKsp Practice 1
  • SolubilityKsp Practice 2
  • The Common Ion Effect
  • Common Ion Effect
  • Barium Sulfate Ksp = 11 x 10-10
  • The Common Ion Effect (2)
  • The Common Ion Effect (3)
  • The Common Ion Effect (4)
  • The Common Ion Effect (5)
  • The Common Ion Effect (6)
  • Common Ion Effect Practice (3)
  • Factors Affecting Solubility - pH
  • Solubility in more Acidic Solution example solid Mg(OH)2 in wa
  • Solubility in more Acidic Solution example solid Mg(OH)2 in p
  • Acidic solution example Ag3PO4
  • Acidic solution example AgCl
  • Solubility and Acidity
  • Precipitation and Qualitative Analysis Section 162
  • Precipitation and Qualitative Analysis
  • Precipitation and Qualitative Analysis (2)
  • Precipitation and Qualitative Analysis (3)
  • Precipitation and Qualitative Analysisndash Practice
  • Separating Metal Ions Cu2+ Ag+ Pb2+
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separating Salts by Differences in Ksp
  • Separating Salts by Differences in Ksp (2)
  • Separations by Difference in Ksp
  • Qualitative Analysis
  • Slide 138
  • Reaction of NH3 with Cu2+(aq)
  • Solubility and Complex Ions
  • Solubility and Complex Ions (2)
  • Solubility and Complex Ions (3)
  • Slide 143
  • Solubility and Complex Ions (4)
  • Solubility and Complex Ions Example
  • Solubility and Complex Ions Example (2)
  • AP Exam Practice