Chapter 6 Problems 6-29, 6-31, 6-39, 6.41, 6-42, 6-48,
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Transcript of Chapter 6 Problems 6-29, 6-31, 6-39, 6.41, 6-42, 6-48,
Chapter 6 Problems
6-29, 6-31, 6-39, 6.41, 6-42, 6-48,
Outline Equilibrium of Acids and Bases
Bronsted-Lowry Acids/Bases Define strong Define weak
pH of pure water at 25oC Define Ka and Kb Relationship b/w Ka and Kb
Chapter 8 – Activity Relationship with K
Acids and Bases & EquilibriumEquilibrium
Section 6-7
Strong Bronsted-Lowry Acid
A strong Bronsted-Lowry Acid is one that donates all of its acidic protons to water molecules in aqueous solution. (Water is base – electron donor or the proton acceptor).
Strong Bronsted-Lowry Base
Accepts protons from water molecules to form an amount of hydroxide ion, OH-, equivalent to the amount of base added.
Question
Can you think of a salt that when dissolved in water is not an acid nor a base?
Weak Bronsted-Lowry acid
One that DOES not donate all of its acidic protons to water molecules in aqueous solution.
Example?
Weak Bronsted-Lowry base
Does NOT accept an amount of protons equivalent to the amount of base added, so the hydroxide ion in a weak base solution is not equivalent to the concentration of base added.
example:
Common Classes of Weak Acids and Bases
Weak Acids
Weak Bases
Question: Question: Calculate the Concentration of H+ and OH- in Pure
water at 250C.
Equilibrium and Equilibrium and WaterWater
EXAMPLE: Calculate the Concentration of H+ and OH- in Pure water at 250C.
H2O H+ + OH-
KW=
Kw =
EXAMPLE: Calculate the Concentration of H+ and OH- in Pure water at 250C.
H2O H+ + OH-
KW=
Kw =
Example
What is the concentration of OH- in a solution of water that is 1.0 x 10-3 M in [H+] (@ 25 oC)?
Kw = [H+][OH-]
1.0 x 10-14 = [1 x 10-3][OH-]
1.0 x 10-11 = [OH-]
“From now on, assume the temperature to be 25oC unless otherwise stated.”
pH
~ -3 -----> ~ +16pH + pOH = - log Kw = pKw = 14.00
Weak Acids and Bases
HA H+ + A-
HA + H2O(l) H3O+ + A-
Ka
Weak Acids and Bases
B + H2O BH+ + OH-Kb
Relation Between KRelation Between Kaa and and KKbb
Relation between Ka and Kb
Consider Ammonia and its conjugate acid.
NH3 + H2O NH4+ + OH-
Kb
NH4+ + H2O NH3 + H3O+
Ka
Example
The Ka for acetic acid is 1.75 x 10-5. Find Kb for its conjugate base.
Example Calculate the hydroxide ion concentration in
a 0.0100 M sodium hypochlorite solution.OCl- + H2O HOCl + OH-
The acid dissociation constant = 3.0 x 10-8
][
]][[
OCl
OHHOClKb
1st Insurance Problem
Challenge on page 120Challenge on page 120
Chapter 8
ActivityActivity
Write out the equilibrium constant for the following expression
Fe3+ + SCN- Fe(SCN)2+
Q: What happens to K when we add, say KNO3 ?
]][[
])([3
2
SCNFe
SCNFeK
K decreases when an inert salt is added!!! Why?
Keq
8-1 Effect of Ionic Strength 8-1 Effect of Ionic Strength on Solubility of Saltson Solubility of Salts
Consider a saturated solution of Hg2(IO3)2 in ‘pure water’. Calculate the concentration of mercurous ions.
Hg2(IO3)2(s) Hg22+ + 2IO3
- Ksp=1.3x10-18
A seemingly strange effectseemingly strange effect is observed when a salt such as KNO3 is added. As more KNO3 is added to the solution, more
solid dissolves until [Hg22+] increases to 1.0 x 10-6 M. Why?
1823
22 103.1]][[ IOHgK sp
IICCEE
somesome -- - --x-x +x+x +2x+2xsome-xsome-x +x+x +2x+2x
182 103.1]2][[ xxK sp7109.6][ x
Increased solubility
Why? LeChatelier’s Principle?
Complex Ion?
?
The potassium hydrogen tartrate example
K+-O
O
OH
OH
O
OH
potassium hydrogen tartrate
Alright, what do we mean by Ionic strength?
Ionic strength is dependent on the number of ions in solution and their charge.
Ionic strength () = ½ (c1z12+ c2z2
2 + …)
Or Ionic strength (m) = ½ cizi2
Examples Calculate the ionic strength of (a) 0.1 M
solution of KNO3 and (b) a 0.1 M solution of
Na2SO4 (c) a mixture containing 0.1 M KNO3
and 0.1 M Na2SO4.() = ½ (c1z1
2+ c2z22 + …)
Alright, that’s great but how does it affect the equilibrium constant?
Activity = Ac = [C]c
AND
bB
baA
a
dD
dcC
c
bB
aA
dD
cC
BA
DC
AA
AAK
][][
][][
Relationship between activity and ionic strength
x
x
xz
3.31
51.0log
2
Debye-Huckel Equation
2 comments
= ionic strength of solution = activity coefficientZ = Charge on the species x = effective diameter of ion (nm)
(1)What happens to when approaches zero?(2)Most singly charged ions have an effective radius of about 0.3 nm
Anyway … we generally don’t need to calculate – can get it from a table
Activity coefficients are Activity coefficients are related to the hydrated related to the hydrated radius of atoms in radius of atoms in moleculesmolecules
Relationship between and
Back to our original problem
Consider a saturated solution of Hg2(IO3)2 in ‘pure water’. Calculate the concentration of mercurous ions.
Hg2(IO3)2(s) Hg22+ + 2IO3
- Ksp=1.3x10-18
Back to our original problem
Consider a saturated solution of Hg2(IO3)2 in ‘pure water’. Calculate the concentration of mercurous ions.
Hg2(IO3)2(s) Hg22+ + 2IO3
- Ksp=1.3x10-18
In 0.1 M KNO3 - how much Hg22+ will be dissolved?
Back to our original problem
Consider a saturated solution of Hg2(IO3)2 in ‘pure water’. Calculate the concentration of mercurous ions.
Hg2(IO3)2(s) Hg22+ + 2IO3
- Ksp=1.3x10-18