CHAPTER 14: Acid / Base Equilibria
Useful tables:
Values of Ka for Some Common Monoprotic Acids
Name
Formula
Ka
Hydrogen sulfate ion
HSO41.2 × 10-2
Chlorous acid
HClO2
1.2 × 10-2
Monochloracetic acid
HC2H2ClO2
1.35 × 10-3
Hydrofluoric acid
HF
7.2 × 10-4
Nitrous acid
HNO2
4.0 × 10-4
Acetic acid
HC2H3O2
1.8 × 10-5
+3
Hydrated aluminum(III) ion
[Al3(H2O)6]
1.4 × 10-5
Hypochlorous acid
HOCl
3.5 × 10-8
Hydrocyanic acid
HCN
6.2 × 10-10
Ammonium ion
NH4+
5.6 × 10-10
Pheno
HOC6H5
1.6 × 10-10
Name
Ammonia
Methylamine
Ethylamine
Aniline
Pyridine
Values of Kb for Some Common Weak Bases
Formula
Conjugate Acid
NH3
NH4+
CH3NH2
CH3NH3+
C2H5NH2
C2H5NH3+
C6H5NH2
C6H5NH3+
C5H5N
C5H5NH+
Kb
1.8 × 10-5
4.38 × 10-4
5.6 × 10-4
3.8 × 10-10
1.7 × 10-9
1. Define each of the following.
a. Arrhenius acid
b. Brønsted-Lowry acid
c. Lewis acid
Which of the definitions is most general? Write reactions to justify your answer.
2. Give the conditions for a neutral solution at 25ºC, in terms of [H+], pH, and the
relationship between [H+] and [OH-].
3. For oxyacids, how does acid strength depend on
a. strength of the bond to the acidic hydrogen atom?
b. electronegativity of the element bonded to the oxygen atom that bears the acidic
hydrogen?
c. the number of oxygen atoms?
4. In terms of orbitals and electron arrangements, what must be present for a molecule or
an ion to act as a Lewis acid? What must be present for a molecule or an ion to act as a
Lewis base?
5. CH3CO2H(aq) + H2O(l) ↔ CH3CO2-(aq) + H3O(aq)
where Ka = 1.8 × 10-5a. Which two bases are competing for the proton?
b. Which is the stronger base?
c. In light of your answer to b, why do we classify the acetate ion (CH3CO2-) as a
weak base? Use an appropriate reaction to justify your answer.
6. Write the dissociation reaction and the corresponding Ka equilibrium expression for each
of the following acids in water.
a. HC2H3O2
b. Co(H2O)6+3
c. CH3NH3+
7. For each of the following aqueous reactions, identify the acid, the base, the conjugate
base, and the conjugate acid.
a. HF + H2O ↔ F- + H3O+
b. H2SO4 + H2O ↔ H3O+ + HSO4-
c. HSO4- + H2O ↔ SO42- + H3O+
8. For each of the following aqueous reactions, identify the acid, the base, the conjugate
base, and the conjugate acid.
a. Al(H2O)6+3 + H2O ↔ H3O+ + Al(H2O)5(OH)+2
b. H2O + HONH3+ ↔ HONH2 + H3O+
c. HOCl + C6H5NH2 ↔ OCl- + C6H5NH3+
9. Use a table to order the following from the strongest to the weakest base:
H2O
NO3OClNH3
10. You may need a table to answer the following questions.
a. Which is the stronger base, Cl- or H2O?
b. Which is the stronger base, H2O or NO2-?
c. Which is the stronger base, CN- or OC6H5-?
11. Calculate the [H+] of each of the following solutions at 25ºC. Identify each solution as
neutral, acidic, or basic.
a. [OH-] = 3.6 M
c. [OH-] = 2.2 × 10-3 M
b. [OH-] = 9.7 × 10-9 M
d. [OH-] = 1.0 × 10-7 M
12. Values of Kw as a function of temperature are as follows:
Temperature (ºC)
Kw
0
1.14 × 10-15
25
1.00 × 10-14
35
2.09 × 10-14
40.
2.92 × 10-14
50.
5.47 × 10-14
a. Is the autoionization of water exothermic or endothermic?
b. Calculate [H+] and [OH-] in a neutral solution at 50ºC.
13. Calculate [H+] and [OH-] for each solution at 25ºC. Identify each solution as neutral,
acidic, or basic.
a. pH = 7.40 (the normal pH of blood)
b. pH = 15.3
c. pH = -1.0
d. pH = 3.20
e. pH =5.0
f. pH = 9.60
14. The pOH of a sample of baking soda dissolved in water is 5.74 at 25ºC. Calculate the
pH, [H+], and [OH-] for this sample. Is the solution acidic or basic?
15. Write the reaction and the corresponding Kb equilibrium expression for each of the
following substances acting as bases in water.
a. Aniline, C6H5NH2
b. dimethylamine, (CH3)2NH
16. Use a table to help order the following bases from strongest to weakest.
NO3H2O
NH3
C5H5N
17. Calculate the pH of the following solutions.
a. 0.10 M NaOH
b. 1.0 × 10-10 M NaOH
c. 2.0 M NaOH
18. For the reaction of hydrazine (N2H4) in water,
H2NNH2(aq) + H2O(l) ↔ H2NNH3+(aq) + OH-(aq)
Kb is 3.0 × 10-6. Calculate the concentrations of all species and the pH of
a 2.0 M solution of hydrazine in water.
19. Calculate the percent ionization in each of the following solutions (see a table for Kb
values).
a. 0.10 M hydroxylamine (HONH2, Kb = 1.0 ×10-8)
b. 0.10 M methylamine (CH3NH2)
20. Write out the stepwise Ka reactions for citric acid (H3C6H5O7), a triprotic acid.
21. Calculate the pH of a 2.0 M H2SO4 solution.
22. Calculate the pH of a 5.0 × 10-3 M solution of H2SO4.
23. Arrange the following 0.10 M solutions in order of most acidic to most basic:
KOH
KCl
KCN
NH4Cl
HCl
24. Given that the Ka value for acetic acid is 1.8 × 10-5 and the Ka value for hypochlorous
acid is 3.5 × 10-8, which is the stronger base, OCl- or C2H3O2-?
25. Calculate the pH of each of the following solutions.
a. 0.12 M KNO2
b. 0.45 M NaOCl
c. 0.40 M NH4ClO4
26. Place the species in each of the following groups in order of increasing acid strength.
Explain the order you chose for each group.
a. HIO3, HBrO3
b. HNO2, HNO3
c. HOCl, HOI
d. H3PO4, H3PO3
27. Will the following oxides give acidic, basic, or neutral solutions when dissolved in water?
Write reactions to justify your answers.
a. Li2O
b. CO2
c. SrO
Answers:
11. a.) 2.8 ×10-15 M; b.) 1.0 × 10-6 M; c.) 4.5 × 10-12 M; d.) 1.0 × 10-7 M
12. b.) 2.34 × 10-7 M
13. a.) pOH = 6.60, [H+] = 4.0 × 10-8 M, [OH-] = 2.5 × 10-7 M; b.) pOH = -1.3, [H+] = 5 × 10-16 M,
[OH-] = 20 M; c.) pOH = 15.0, [H+] = 10 M, [OH-] = 1 × 10-15 M; d.) pOH = 10.80, [H+] = 6.3 × 10-4
M, [OH-] = 1.6 × 10-11 M; e.) pH = 9.0, [H+] = 1 × 10-9 M, [OH-] = 1 × 10-5 M; f.) pH = 4.40, [H+] =
4.0 × 10-5 M, [OH-] = 2.5 × 10-10 M
14. pH = 8.26, [H+] = 5.5 × 10-9 M, [OH-] = 1.8 × 10-6 M
17. a.) pH = 13.00; b.) pH = 7.00; c.) pH = 14.30
18. [H2NNH3+] = 2.4 × 10-3 M, [H2NNH2] = 2.0 M, [H+] = 4.2 × 10-12 M
19. a.) 0.033 %; b.) 6.4 %
21. pH = -0.30
22. pH = 2.10
25. a.) pH = 8.23; b.) pH = 10.56; c.) pH = 4.82
*Questions taken from Zumdahl & Zumdahl’s Chemistry; Sixth Edition