Chapter 16 – Acid-Base Equilibria
1. For which of the following equilibria does Kc correspond to an acid-ionization constant, Ka?
A)
NH3(aq) + H3O+(aq) NH4+(aq) + H2O(l)
B)
NH4+(aq) + OH–(aq) NH3(aq) + H2O(l)
C)
F–(aq) + H2O(l) HF(aq) + OH–(aq)
D)
HF(aq) + OH–(aq) H2O(l) + F–(aq)
E)
NH4+(aq) + H2O(l) NH3(aq) + H3O+(aq)
2. Which of the following is/are true concerning the acid-ionization of a monoprotic weak
acid?
1.
The products of an acid-ionization include the hydronium ion (hydrogen ion)
or hydroxide ion.
2.
The percent ionization of a weak acid is greatest for the most dilute solution.
3.
A weak acid ionization constant is only valid in an aqueous solvent.
A)
1 only
B)
2 only
C)
3 only
D)
2 and 3
E)
1, 2, and 3
3. For which of the following equilibria does Kc correspond to the acid-ionization constant, Ka,
of HCO3–?
A)
HCO3–(aq) + OH–(aq) CO32–(aq) + H2O(l)
B)
H2CO3(aq) + H2O(l) HCO3–(aq) + H3O+(aq)
C)
HCO3–(aq) + H2O(l) H2CO3(aq) + OH–(aq)
D)
HCO3–(aq) + H3O+(aq) H2CO3(aq) + H2O(l)
E)
HCO3–(aq) + H2O(l) CO32–(aq) + H3O+(aq)
Test Bank General Chemistry, 10th edition 2
4. For which of the following equilibria does Kc correspond to the acid-ionization constant, Ka,
of HC2O4–?
A)
HC2O4–(aq) + H2O(l) H2C2O4(aq) + OH–(aq)
B)
H2C2O4(aq) + H2O(l) H3O+(aq) + HC2O4–(aq)
C)
HC2O4–(aq) + H2O(l) H3O+(aq) + C2O42–(aq)
D)
HC2O4–(aq) + OH–(aq) C2O42–(aq) + H2O(l)
E)
HC2O4–(aq) + H3O+(aq) H2C2O4(aq) + H2O(l)
5. For which of the following equilibria does Kc correspond to the acid-dissociation constant,
Ka, of H2PO4–?
A)
H2PO4–(aq) + H3O+(aq) H3PO4(aq) + H2O(l)
B)
H2PO4–(aq) + H2O(l) H3PO4(aq) + OH–(aq)
C)
H2PO4–(aq) + H2O(l) H3O+(aq) + HPO42–(aq)
D)
H3PO4(aq) + H2O(l) H3O+(aq) + H2PO4–(aq)
E)
HPO42–(aq) + H2O(l) H2PO4–(aq) + OH–(aq)
6. What is the equilibrium expression for the equilibrium A–(aq) + H3O+(aq) HA(aq) +
H2O(l)?
A)
B)
C)
D)
E)
Kb
Test Bank General Chemistry, 10th edition 3
7. For the equilibrium that exists in an aqueous solution of nitrous acid (HNO2, a weak acid),
the equilibrium-constant expression is
A)
K = .
B)
K = .
C)
K = .
D)
K = [H+][NO2–].
E)
none of these
8. Consider the Ka values for the following acids:
Cyanic acid, HOCN, 3.5 10–4
Formic acid, HCHO2, 1.7 10–4
Lactic acid, HC3H5O3, 1.3 10–4
Propionic acid, HC3H5O2, 1.3 10–5
Benzoic acid, HC7H5O2, 6.3 10–5
Which has the strongest conjugate base?
A)
propionic acid
B)
benzoic acid
C)
lactic acid
D)
formic acid
E)
cyanic
9. Consider the Ka values for the following acids:
Cyanic acid, HOCN, 3.5 10–4
Formic acid, HCHO2, 1.7 10–4
Lactic acid, HC3H5O3, 1.3 10–4
Propionic acid, HC3H5O2, 1.3 10–5
Benzoic acid, HC7H5O2, 6.3 10–5
Given initially equimolar soutions of each weak acid, which solution will have the highest
hydronium ion concentration once equilibrium is established?
Test Bank General Chemistry, 10th edition 4
A)
cyanic acid
B)
benzoic acid
C)
lactic acid
D)
formic acid
E)
propionic acid
10. Rank acetic acid (HC2H3O2), hydrocyanic acid (HOCN), and hydrofluoric acid (HF) in
order of increasing strength.
Acid
Ka
HC2H3O2
1.8 10–5
HOCN
3.5 10–4
HF
6.8 10–4
A)
HC2H3O2 < HOCN < HF
B)
HOCN < HC2H3O2 < HF
C)
HOCN < HF < HC2H3O2
D)
HF < HOCN < HC2H3O2
E)
HF < HC2H3O2 < HOCN
11. What is the percent ionization of a 1.8 M HC2H3O2 solution (Ka = 1.8 10–5 ) at 25°C?
A)
0.57 %
B)
0.32 %
C)
2.2 %
D)
0.18 %
E)
0.24 %
12. A 0.20 M solution of a weak monoprotic acid is 0.18 % ionized. What is the acid-ionization
constant, Ka, for this acid?
A)
1.3 10–6
B)
1.8 10–6
C)
0.9 10–4
D)
1.6 10–5
E)
6.5 10–7
Test Bank General Chemistry, 10th edition 5
13. What is the pH of an initially 0.580 M solution of a weak monoprotic acid that is 0.24 %
ionized when equilibrium is established? (assume Ca/Ka 102)
A)
2.85
B)
7.00
C)
0.85
D)
9.12
E)
11.15
14. At a temperature of 25C an initally 0.048 M solution of a weak monoprotic acid is 2.7 %
ionized once equilibrium is established. What is the acid-ionization constant, Ka, for this
acid? (assume Ca/Ka 102)
A)
3.5 10−5
B)
1.7 10−6
C)
2.3 10−1
D)
1.5 102
E)
1.7 10−7
15. Equal moles of the indicated acids are dissolved in the amounts of water shown in the
beakers below. In which solution will the percent ionization of the acid be the lowest?
Test Bank General Chemistry, 10th edition 6
A)
All have equal percent ionization of acid.
B)
III
C)
IV
D)
II
E)
I
16. A 0.010 M aqueous solution of a weak acid HA has a pH of 5.0. What is the degree of
ionization of HA in the solution?
A)
1 %
B)
0.01 %
C)
10 %
D)
0.1 %
E)
0.001 %
17. A 7.5 10-3 M solution of acetic acid, HC2H3O2, is 4.9% ionized at 25°C. In a 7.5 10-4 M
solution, the percentage of ionization would be
A)
100%.
B)
<4.9%.
C)
>4.9%.
D)
the same.
E)
zero.
18. A 0.10 M aqueous solution of a weak acid HA has a pH of 5.00. What is the value of Ka for
HA?
A)
1.0 10–8
B)
1.0 10–6
C)
1.0 10–7
D)
1.0 10–5
E)
1.0 10–9
19. An initially 2.2 M aqueous solution of a weak monoprotic acid has a total ion concentration
of
1.31 10−2
M when equilibrium is established. What is the acid-ionization constant, Ka,
of the weak acid? (assume Ca/Ka 102)
A)
2.0 10−5
B)
1.7 10−4
C)
1.3 10−1
D)
4.1 10−2
E)
9.9 10−8
20. A 0.10 M solution of a weak monoprotic acid has a hydronium-ion concentration of
4.2 10–4 M. What is the acid-ionization constant, Ka, for this acid?
A)
2.0 10–2
B)
2.9 10–3
C)
4.2 10–4
D)
1.8 10–6
E)
5.0 10–5
21. A 0.10 M solution of a weak monoprotic acid has a pH of 3.40 at 25°C. What is the acid-
ionization constant, Ka, for this acid?
A)
1.6 10–6
B)
4.0 10–4
C)
3.4 10–5
D)
1.2 10–3
E)
1.8 10–7
Test Bank General Chemistry, 10th edition 8
22. What is Ka for a weak monoprotic acid if a 0.020 M solution of the acid has a pH of 3.23 at
25°C?
A)
5.9 10–2
B)
1.7 10–5
C)
7.8 10–2
D)
1.2 10–6
E)
3.5 10–4
23. The equilibrium hydronium ion concentration of an initially 0.150 M solution of a
monoprotic weak acid is
1.4 10−3
M. The acid dissociation constant is
1.31 10−5
at 25°C.
What is the pH of this solution?
A)
2.85
B)
7.00
C)
11.15
D)
5.71
E)
0.82
24. What is the equilibrium percent ionization of an initially 0.40 M solution of the monoprotic
acid propanoic acid, HC3H5O2, at 25°C (Ka =
1.34 10−5
)?
A)
0.58%
B)
1.2%
C)
0.0013%
D)
0.13%
E)
1.4%
25. What is the hydronium-ion concentration of a 0.30 M solution of HCN (Ka = 4.9 10–10) at
25°C?
A)
1.7 10–4 M
B)
3.4 10–6 M
C)
2.2 10–6 M
D)
1.2 10–5 M
E)
4.0 10–5 M
26. What is the equilibrium pH of an initially 0.26 M solution of the monoprotic acid hydrazoic
acid at 25°C (Ka =
2.2 10−5
)?
A)
2.62
B)
7.00
C)
2.32
D)
11.68
E)
4.68
27. What is the equilibrium hydronium ion concentration of an initially 4.2 M solution of
hypochlorous acid, HOCl, at 25°C (Ka =
3.0 10−8
)?
A)
3.5 10−4
M
B)
2.3 10−7
M
C)
2.5 10−4
M
D)
5.0 10−4
M
E)
8.5 10−5
M
28. What is the equilibrium pH of an initially 5.1 M solution of hypoiodous acid, HOI, at 25°C
(Ka =
2.3 10−11
)?
A)
4.97
B)
7.00
C)
5.12
D)
4.81
E)
8.33
29. It is safe to make the simplifying assumption that x can be neglected in the denominator of
the equilibrium equation when
A)
.
B)
.
C)
.
D)
.
E)
.
30. What is the equilibrium concentration of chloroacetic acid, HC2H2O2Cl, in a solution
prepared by dissolving 0.0221 mol of HC2H2O2Cl in 1.20 L of water? For chloroacetic acid,
Ka = 1.4 10–3.
A)
4.43 10–3 M
B)
1.84 10–2 M
C)
5.08 10–3 M
D)
1.40 10–2 M
E)
9.21 10–3 M
31. What is the pH of a solution prepared by dissolving 0.0265 mol of chloroacetic acid,
(HC2H2O2Cl) in 1.30 L of water? For chloroacetic acid, Ka = 1.4 10–3.
A)
1.69
B)
2.33
C)
11.67
D)
12.31
E)
2.27
32. What is the percent ionization of a solution prepared by dissolving 0.0111 mol of
chloroacetic acid, (HC2H2O2Cl) in 1.80 L of water? For chloroacetic acid, Ka = 1.4 10–3.
A)
0.62 %
B)
100 %
C)
38 %
D)
62 %
E)
0.23 %
33. A 8.80-g sample of homogentisic acid, a weak organic acid having Ka = 4.0 10–5, is
dissolved in 25.00 mL of water and its pH is measured to be 2.039. What is the molar mass
of homogentisic acid?
A)
168 g/mol
B)
964 g/mol
C)
2.09 g/mol
D)
4.20 g/mol
E)
352 g/mol
34. Which of the following represents the usual relationship of acid-ionization constants for a
triprotic acid?
A)
B)
C)
D)
E)
35. Phosphoric acid, H3PO4, will undergo three successive ionization reactions to varying
extents in water. What is the balanced equilibrium identified as Ka3?
A)
H2PO4–(aq) + H2O(l) H3O+(aq) + HPO42–(aq)
B)
HPO42–(aq) + H2O(l) PO43–(aq) + H3O+(aq)
C)
H2PO4–(aq) + H3O+(aq) H3PO4(aq) + H2O(l)
D)
H3PO4(aq) + H2O(l) H3O+(aq) + H2PO4–(aq)
E)
PO43–(aq) + H2O(l) HPO42–(aq) + OH–(aq)
36. In a 0.01 M solution of 1,4-butanedicarboxylic acid, HOOCCH2CH2COOH (Ka1 = 2.9 10–
5, Ka2 = 5.3 10–6), which species is present in the highest concentration?
A)
HOOCCH2CH2COO–(aq)
B)
HOOCCH2CH2COOH(aq)
C)
H3O+(aq)
D)
–OOCCH2CH2COO–(aq)
E)
OH–(aq)
37. In a 0.01 M solution of 1,4-butanedicarboxylic acid, HOOCCH2CH2COOH (Ka1 = 2.9 10–
5, Ka2 = 5.3 10–6), which species is present in the lowest concentration?
A)
–OOCCH2CH2COO–(aq)
B)
H2O
C)
HOOCCH2CH2COO–(aq)
D)
H3O+(aq)
E)
HOOCCH2CH2COOH(aq)
38. For a 0.05 M H2SO3 solution, which of the following relationships is true?
A)
[SO32–] > [H2SO3]
B)
[SO32–] > [HSO3–]
C)
[HSO3–] > [H2SO3]
D)
[H2SO3] > [H+]
E)
[H+] > [H2SO3]
39. Hydrosulfuric acid, H2S, is a weak diprotic acid. In a 0.1 M solution of the acid, which of
the following species is present in the largest amount?
A)
HS–
B)
S2–
C)
H2S
D)
H3O+
E)
OH–
40. For a 0.10 M solution of glutaric acid, HO2C(CH2)3CO2H (Ka1 = 4.6 10–5, Ka2 = 3.9 10–
6), rank the following species in order of increasing equilibrium concentration.
A)
H3O+ < –O2C(CH2)3COO– < HO2C(CH2)3COO– < OH– < HO2C(CH2)3CO2H
B)
OH– < –O2C(CH2)3COO– < H3O+ < HO2C(CH2)3COO– < HO2C(CH2)3CO2H
C)
OH– < –O2C(CH2)3COO– < HO2C(CH2)3COO– < H3O+ < HO2C(CH2)3CO2H
D)
H3O+ < HO2C(CH2)3CO2H < HO2C(CH2)3COO– < –O2C(CH2)3COO– < OH–
E)
OH– < –O2C(CH2)3COO– < HO2C(CH2)3COO– < HO2C(CH2)3CO2H < H3O+
41. Which of the following is/are true concerning multiprotic acids where Ka1 >> Ka2?
1.
In a solution made from H3A, the equilibrium concentration of H3O+ and
H2A− can be accurately determined from the first ionization without
accounting for the remaining ionizations.
2.
In a solution made from H2A, the equilibrium concentration of the fully
deprotonated form of the acid (A2-) is approximately equal to Ka1.
3.
In general the second ionization constant of a triprotic acid is nearly equal to
the third ionization constant and both are much smaller than the first
ionization constant.
A)
1 only
B)
2 only
C)
3 only
D)
1 and 3
E)
1, 2, and 3
42. Two unlabeled solutions are found to have a pH of 4.00. Which of the following is/are
reasonable conclusions regarding the composition of each solution?
1.
The molar concentration of H3O+ is the same in both solutions.
2.
The relatively high pH compared to a solution of strong acid is consistent with
neither solution containing a strong acid.
3.
One or both solutions may contain a weak monoprotic or multiprotic acid.
A)
1 only
B)
2 only
C)
3 only
D)
1 and 3
E)
1, 2, and 3
43. In a 0.10 M solution of a diprotic acid H2A (Ka1 = 3.6 10–5 and Ka2 = 9.8 10–10 at 25°C),
what is the equilibrium concentration of A2–?
A)
9.9 10–6 M
B)
9.8 10–10 M
C)
1.9 10–3 M
D)
0.20 M
E)
0.10 M
44. The equilibrium hydronium ion concentration of an initially 0.228 M solution of a diprotic
weak acid (H2A) is
1.9 10−3
M. What is Ka1? (assume Ca/Ka 102 and Ka1 >> Ka2)
A)
1.6 10−5
B)
2.3 10−6
C)
3.0 10−8
D)
3.6 10−6
E)
not enough information provided
Test Bank General Chemistry, 10th edition 15
45. What is the hydronium-ion concentration in a 0.030 M solution of carbonic acid, H2CO3?
For carbonic acid, Ka1 = 4.2 10–7 and Ka2 = 4.8 10–11.
A)
3.0 10–2 M
B)
4.2 10–7 M
C)
4.8 10–11 M
D)
1.1 10–4 M
E)
5.6 10–5 M
46. What is the concentration of HCO3– in a 0.029 M solution of carbonic acid, H2CO3? For
carbonic acid, Ka1 = 4.2 10–7 and Ka2 = 4.8 10–11.
A)
1.1 10–4 M
B)
2.9 10–2 M
C)
5.5 10–5 M
D)
4.8 10–11 M
E)
4.2 10–7 M
47. What is the concentration of CO32– in a 0.030 M solution of carbonic acid, H2CO3? For
carbonic acid, Ka1 = 4.2 10–7 and Ka2 = 4.8 10–11.
A)
3.0 10–2 M
B)
1.1 10–4 M
C)
5.6 10–5 M
D)
4.8 10–11 M
E)
4.2 10–7 M
48. What is the hydronium-ion concentration of a 0.350 M oxalic acid, H2C2O4, solution? For
oxalic acid, Ka1 = 5.6 10–2 and Ka2 = 5.1 10–5.
A)
1.1 10–1 M
B)
1.4 10–1 M
C)
1.0 10–7 M
D)
4.2 10–3 M
E)
4.2 10–3 M
49. What is the hydroxide-ion concentration of a 0.240 M oxalic acid, H2C2O4, solution? For
oxalic acid, Ka1 = 5.6 10–2 and Ka2 = 5.1 10–5.
A)
2.9 10–12 M
B)
8.6 10–14 M
C)
3.5 10–3 M
D)
1.1 10–13 M
E)
1.0 10–7 M
50. What is the concentration of HC2O4– in a 0.390 M oxalic acid, H2C2O4, solution? For oxalic
acid, Ka1 = 5.6 10–2 and Ka2 = 5.1 10–5.
A)
4.4 10–3 M
B)
1.2 10–1 M
C)
1.5 10–1 M
D)
4.5 10–3 M
E)
5.1 10–5 M
51. What is the concentration of C2O42– in a 0.370 M oxalic acid, H2C2O4, solution? For oxalic
acid, Ka1 = 5.6 10–2 and Ka2 = 5.1 10–5.
A)
1.2 10–1 M
B)
4.3 10–3 M
C)
4.3 10–3 M
D)
5.1 10–5 M
E)
1.4 10–1 M
Test Bank General Chemistry, 10th edition 17
52. What is the equilibrium concentration of H2C2O4 in a 0.230 M oxalic acid, H2C2O4,
solution? For oxalic acid, Ka1 = 5.6 10–2 and Ka2 = 5.1 10–5.
A)
1.4 10–1 M
B)
1.1 10–1 M
C)
2.3 10–1 M
D)
5.1 10–5 M
E)
8.9 10–2 M
53. For which of the following equilibria does Kc correspond to a base-ionization constant, Kb?
A)
H3O+(aq) + OH–(aq) 2H2O(l)
B)
HCO3–(aq) + OH–(aq) CO32–(aq) + H2O(l)
C)
HOCl(aq) + H2O(l) H3O+(aq) + OCl–(aq)
D)
CO32–(aq) + H2O(l) HCO3–(aq) + OH–(aq)
E)
HCHO2(aq) + NH3(aq) CHO2–(aq) + NH4+(aq)
54. For which of the following equilibria does Kc correspond to the base-ionization constant, Kb,
of HCO3–?
A)
HCO3–(aq) + H2O(l) CO32–(aq) + H3O+(aq)
B)
HCO3–(aq) + H2O(l) H2CO3(aq) + OH–(aq)
C)
H2CO3(aq) + H2O(l) HCO3–(aq) + H3O+(aq)
D)
HCO3–(aq) + OH–(aq) CO32–(aq) + H2O(l)
E)
HCO3–(aq) + H3O+(aq) H2CO3(aq) + H2O(l)
55. Which of the following reactions is associated with the definition of Kb?
A)
CN–(aq) + H+(aq) HCN(aq)
B)
F–(aq) + H2O(l) HF(aq) + OH–(aq)
C)
Zn(OH2)62+(aq) [Zn(OH2)5OH]+(aq) + H+(aq)
D)
Cr3+(aq) + 6H2O(l) Cr(OH2)63+(aq)
E)
none of these
56. What is the base-ionization equilibrium constant for an aqueous solution of ammonia, NH3?
A)
B)
C)
D)
E)
none of these
57. What is the pOH of a 0.20 M solution of pyridine (Kb = 1.4 10–9) at 25°C?
A)
1.40
B)
4.08
C)
8.85
D)
4.78
E)
11.00
58. What is the pH of a 0.24 M solution of methylamine (CH3NH2, Kb = 4.4 10–4) at 25oC?
A)
5.63
B)
0.62
C)
12.00
D)
13.38
E)
2.00
Test Bank General Chemistry, 10th edition 19
59. What is the hydronium-ion concentration at equilibrium in a 0.72 M solution of aniline
(C6H5NH2, Kb = 4.2 10–10) at 25oC?
A)
1.4 10–14 M
B)
7.2 10–1 M
C)
5.8 10–10 M
D)
1.7 10–5 M
E)
2.4 10–5 M
60. What is the hydroxide-ion concentration at equilibrium in a 0.17 M solution of ethylamine
(C2H5NH2, Kb = 4.7 10–4) at 25oC?
A)
8.7 10–3 M
B)
5.4 10–2 M
C)
5.9 10–14 M
D)
1.1 10–12 M
E)
1.7 10–1 M
61. What is the percent ionization at equilibrium in a 0.75 M solution of dimethylamine,
(CH3)2NH (Kb = 5.1 10–4), at 25oC?
A)
2.6%
B)
0.068%
C)
1.9%
D)
100%
E)
75%
62. What is the equilibrium concentration of ammonium ion in a 0.51 M solution of ammonia
(NH3, Kb = 1.8 10–5) at 25oC?
A)
2.0 10–14 M
B)
3.3 10–12 M
C)
3.0 10–3 M
D)
6.0 10–3 M
E)
5.1 10–1 M
Test Bank General Chemistry, 10th edition 20
63. A solution of aniline (C6H5NH2, Kb = 4.2 10–10) has a pH of 8.75 at 25oC. What was the
initial concentration of aniline?
A)
1.8 10–9 M
B)
9.3 10–9 M
C)
7.7 10–2 M
D)
4.2 10–10 M
E)
5.6 10–6 M
64. A 0.0884 M solution of a weak base has a pH of 11.79. What is the identity of the weak
base?
Weak Base
Kb
Ethylamine (CH3CH2NH2)
4.7 10–4
Hydrazine (N2H4)
1.7 10–6
Hydroxylamine (NH2OH)
1.1 10–8
Pyridine (C5H5N)
1.4 10–9
Aniline (C6H5NH2)
4.2 10–10
A)
hydrazine
B)
pyridine
C)
aniline
D)
ethylamine
E)
hydroxylamine
65. Saccharin is a weak organic base with a Kb of 4.80 10–3. A 0.297-g sample of saccharin
dissolved in 25.0 mL of water has a pH of 12.190. What is the molar mass of saccharin?
A)
0.616 g/mol
B)
19.3 g/mol
C)
184 g/mol
D)
181 g/mol
E)
119 g/mol