Ch 6 chemical equilibrium 4.0

Aqueous Solution Chemistry• Review of Chem. I and Chem II

Memorize lists of strong acids-bases

Simple definitionacid – donates a protonbase – accepts a proton

Also know what Lewis acids/bases are,

Memorize

Hydroxides of the alkalineearth metals also consideredto be strong bases

Also note:

Very, very important

Acids/Bases

Conjugate Acids and Bases

HAc + H2O = Ac- + H3O+

Acid Base C. Base C. Acid

NH3 + H2O = NH4+ + OH-

Base Acid C. Acid C. Base

Useful advice: They differ by one and only one proton

Is the acetate ion an acid or base?

Is methylamine an acid or base?

Useful advice: Acids have a proton to lose, bases don’t

Polyprotic acids/bases

Clicker questions

What is the conjugate acid for F-

a. F-2

b. Fc. HFd. H2F

What is the conjugate base for H2PO4-

a. HPO42-

b. H3PO4

c. PO43-

Is H2PO4- an acid or a base

a. Acidb. Basec. Depends

Acids/Bases

Amphiprotic Species– behave as both an acid and a base– ex. H2O is an amphiprotic solvent– ex. H2PO4

-

H2PO4- + H2O = H3PO4 + OH-

H2PO4- + H2O = HPO4

2- + H3O+

Useful advice: the pH of an aqueous solution of anamphiprotic salt is determined by its equilibrium constants

Chemical EquilibriumReaction:

aA + bB = cC + dD


aA + bB = cC + dDK = [C]c [D]d / [A]a [B]b Memorize


aA + bB = cC + dDK = [C]c [D]d / [A]a [B]b

Understood, [C] = [C]/[C]std

solutes: std state = 1 Mgases: std state = 1 barsolids. liq = pure solid, pure liquid

Memorize


aA + bB = cC + dDK = [C]c [D]d / [A]a [B]b

Understood,[C] = [C]/[C]std

solutes: std state = 1 Mgases: std state = 1 barsolids. liq = pure solid, pure liquid

• Make sure all concentrations in M

all gases in bar (atm)pure solids/liquids/solvents are omitted

Types of Equilibrium Constants

A. ion product constant for water2H2O = H3O+ + OH-


A. Ion product constant for water2H2O = H3O+ + OH-

Kw = [H3O+] [OH-] = 1.00 x 10-14

pKw = -log Kw

Memorize



K = [H3O+] [OH-] / [H2O]2

Kw = [H3O+] [OH-] = 1.00 x 10-14

pKw = -log Kw

B. solubility product constantAg2CO3(s) = 2Ag+ + CO3

-2

(temp dependent)



K = [H3O+] [OH-] / [H2O]2

Kw = [H3O+] [OH-] = 1.00 x 10-14

pKw = -log Kw

B. solubility product constantAg2CO3(s) = 2Ag+ + CO3

-2

Ksp = [Ag+]2 [CO3-2] = 8.1 x 10-12

pKsp = -log Ksp


C. Acid Dissociation Constant (Weak Acid)HNO2 + H2O = H3O+ + NO2

-



-

Ka = [H3O+ ] [NO2-] / [HNO2 ]

pKa = -log Ka



-

Ka = [H3O+ ] [NO2-] / [HNO2 ]

pKa = -log Ka

D. Base Dissociation Constant (Weak Base)NH3 + H2O = OH- + NH4

+

Kb = [OH- ] [NH4+] / [NH3 ]

pKb = -log Kb


E. Relationship btwn Ka and Kb conjugate acid base pairs

ex. NH3 and NH4+

NH3 + H2O = OH- + NH4+ Kb = [OH- ] [NH4

+] / [NH3 ]

NH4+ + H2O = H3O+ + NH3 Ka = [H3O+ ] [NH3 ] / [NH4

+ ]

KaKb = Kw Memorize

Useful advice: “a” is for acid, “b” is for base…

Clicker Question:

Which one of the following weak acids will bestronger in water?

a. Acetic acid Ka = 1.75 x 10-5 b. Benzoic acid Ka = 6.28 x 10-5

c. HF Ka = 6.8 x 10-4

d. HCN Ka = 6.2 x 10-10


F. Le Chatelier’s PrincipleSystem will change to relieve the stress

Ex. Ag2CO3(s) = 2Ag+ + CO3-2

Ksp = [Ag+]2 [CO3-2] = 8.1 x 10-12

Disturb the system (Add CO3-2)

Clicker question

A. Shift right (form more products)B. Shift left (form more reactants)

“Common ion effect”


F. Le Chatelier’s PrincipleSystem will change to relieve the stress

Ex. Ag+ + 2NH3 = Ag(NH3)2+ 2 = K1K2

Disturb the system (Add NH3)

Can also set up the reaction quotient, Q

How many grams of barium iodate can be dissolved in 500.0 mL of water at 25 C?

What is the molar solubility of Ag2CO3 in 0.1 M AgNO3

Example Solubility Problems

Ch 6 chemical equilibrium 4.0

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