70 Practice Problems for Ch 7 – Chem 1A
1. For the equilibrium that exists in an aqueous solution of nitrous acid (HNO
2
, a weak acid), the equilibrium constant expression is
A) K = 2
B)
D)
K

C) K = [H + ][NO
2
–
]
K =
2
2
E) none of these
2. Identify the Brønsted acids and bases in the following equation (Answers represent the reaction from left to right).
HPO
4
2 + HSO
4
H
2
PO
4
+ SO
4
2-
A) base, acid, base, acid
B) base, base, acid, acid
C) acid, base, acid, base
D) acid, base, base, acid
E) base, acid, acid, base
3. The equilibrium constant for the reaction is called
A
–
+ H + HA
A) K a
B)
C)
D)
E)
K b
1
K a
K w
K b
K w
K a
4. According to the Brønsted-Lowry definition, an acid is
A) a substance that increases the hydroxide ion concentration in a solution.
B)
C) a substance that increases the hydrogen ion concentration in a solution. a substance that can accept a proton from another species in solution.
D)
E) a substance that can donate a proton to another species. an electron pair acceptor.
5. Which of the following is a conjugate acid-base pair?
A) HCl/OCl
3
–
B) H
3
PO
4
/PO
4
3–
C) NH
D) H
3
4
+
O +
/NH
/OH
3
–
E) Ca 2+ /Ca(OH)
2
6.
A)
B)
Which of the following represents a conjugate acid-base pair?
H
2
PO
HSO
4
–
4
–
and PO
4
3-
C) HNO
3
and SO
and NO
3
2-
3
–
D) HCl and NaOH
E) none of these

7. Which of the following does not represent a conjugate acid-base pair?
A) HF and F -
B) C
5
H
5
NH + and C
5
H
5
N
C) H
3
O + and H
2
O
D) HCN and NH
3
E) none of these
8. Which of the following species is not amphoteric?
A) HSO
B) H
2
4
–
PO
4
–
C) HPO
4
2–
D) H
2
O
E) All of these are amphoteric
9. The hydrogen sulfate or bisulfate ion HSO
4
–
can act as either an acid or a base in water solution. In which of the following equations does HSO
4
–
act as an acid?
A) HSO
4
–
+ H
2
O

H
2
B) HSO
C) HSO
4
–
4
–
+ H
3
O +
SO
4
+ OH

SO
3
+ 2H
2
–
O
D) HSO
4
–
+ OH
– 
H
2
+ H
2
SO
O

SO
4
2–
4
+ O 2–
+ H
3
O +
E) none of these
10. Which of the following is the equilibrium constant expression for the dissociation of the weak acid HOCl?
A) K =
[HOCl]
B) K = [H + ][OCl
–
]
-
C) K =
[HOCl]
+ -
[H ][OCl ]
2-
D) K =
[HOCl]
E) none of these
-
11. The strong acid HA is added to water. Which of the following is the strongest base in the system?
A) HA
B) H
2
O
C) H
D) A
3
–
O +
E) H
2
A
–
12. The conjugate base of a weak acid is
A) a strong base.
B) a weak base.
C) a strong acid.
D) a weak acid.
E) none of these
13. The following acids are listed in order of decreasing acid strength in water.
HI > HNO
2
> CH
3
COOH > HClO > HCN
According to Brønsted-Lowry theory, which of the following ions is the weakest base?
A) I
–
B) NO
2
–
C) CH
3
COO
–
D) ClO
–
E) CN
–

14. In deciding which of two acids is the stronger, one must know
A) the concentration of each acid solution only.
B) the pH of each acid solution only.
C) the equilibrium constant of each acid only.
D) all of the these.
E) both the concentration and the equilibrium constant of each acid.
15. Which reaction does not proceed far to the right?
A) HCl + H
2
O

H
3
O + + Cl
B) H
3
O + + OH
– 
2H
2
O
–
C) H
2
O + HSO

4

H
2
SO
4
+ OH
–
D)
E)
HCN + OH
H
2
SO
4
+ H
2
– 
H
2
O + CN
O

H
3
O +
–
+ HSO

4
16. The acids HC
2
H
3
O
2
and HF are both weak, but HF is a stronger acid than HC
2
H
3
O
2
. HCl is a strong acid.
Order the following according to base strength.
A) C
2
H
3
B) C
C) Cl
D) F
–
2
H
–
3
O
O
> F
2
–
2
–
–
> F
> F
> C
> C
2
H
3
O
–
–
2
2
–
> Cl
–
> H
2
> H
H
3
O
2
2
–
> H
2
O
O > Cl
–
> H
2
O
O > Cl
–
E) none of these
17. At a particular temperature, the ion-product constant of water, K w
, is 2.4

10 -14 . What is the pH of pure water at this temperature?
A) 7.00
B) 7.19
C) 6.56
D) 6.81
E) 6.62
18. For a neutral solution, it must be true that
A) pH = 7.00.
B) [H +
C) [H +
] = 0 M .
] = [OH
–
].
D) [H
2
O] = 1

10 -14
E) At least two of these must be true.
19. Calculate [H + ] in a solution that has a pH of 9.3.
A) 5 M
B) 9 M
C) 5

10
–10
M
D) 2

10
–5
M
E) 1

10
–1
M
20. Find the pH of a solution at 25ºC in which [OH
–
] = 4.3

10
–8
M .
A) 7.37
B) 6.63
C) 8.63
D) 3.70
E) 4.30
21. As water is heated, its pH decreases. This means that
A) the water is no longer neutral.
B) [H + ] > [OH
C) [OH
–
] > [H
–
+
].
].
D) Two of these are correct.
E) None of these is correct.

22. The pH of a solution is raised from 3 to 5. Which of the following statement is false ?
A) The pOH decreases from 11 to 9.
B) The [H + ] decreases by a factor of 20.
C) The final [OH
–
] (at pH = 5) is 10
–9
M .
D) The initial [H + ] (at pH = 3) is 10
–3
M .
E) The initial solution could be 0.001 M HNO
3
.
23. Solid calcium hydroxide is dissolved in water until the pH of the solution is 10.94. What is the hydroxide ion concentration [OH
–
] of the solution?
A) 1.1

10
–11
M
B) 3.06 M
C) 8.7

10
–4
M
D) 1.0

10
–14
M
E) none of these
24. Which of the following indicates the most acidic solution?
A) [OH
–
] = 0.5 M
B) [H + ] = 0.3 M
C) pOH = 5.9
D) pH = 1.2
E) [H + ] = 1.0

10
–4
M
25. HCl gas is in a 1.21-L cylinder at 0.870 atm and 28.0° C. This gas is dissolved in 750.0 mL of water.
Calculate the pH of this solution (assume no volume change).
A) 1.25
B) 1.37
C) 2.52
D) 0.950
E) none of these
26. Calculate the pH of a 1.9 M solution of HNO
3
.
A) 0.28
B) –0.64
C) –0.28
D) 14.28
E) 13.72
27. Calculate the pH of a 0.040 M perchloric acid (HClO
4
) solution.
A) 12.60
B) 11.90
C) 2.10
D) 1.40
E) none of these
28. Calculate the pH of a solution made by mixing equal volumes of a solution of HCl with a pH of 1.44 and a solution of HNO
3
with a pH of 2.74. (Assume the volumes are additive.)
A) 2.09
B) 1.72
C) 4.19
D) 1.42
E) 2.74
29. What concentration of HF ( K a
= 7.2

10
–4
) has the same pH as that of 0.068 M HCl?
A) 6.4 M
B) 0.068 M
C) 4.9

10
–6
M
D) 1.1

10
–2
M
E) 0.16 M
30. The pH of a 0.6 M solution of a weak acid is 4.0. What percent of the acid has ionized?
A) 0.02%
B) 2%

C) 7%
D) 4%
E) 0.06%
31. For nitrous acid, HNO
2
, K a
= 4.0

10
–4
. Calculate the pH of 0.33 M HNO
2
.
A) 1.94
B) 0.48
C) 2.92
D) 4.36
E) 3.40
32. A monoprotic weak acid, when dissolved in water, is 0.92% dissociated and produces a solution with pH =
3.42. Calculate K a
A) 1.4

10
–7
B) 2.8

10
–3
C) 3.5

10
–6
for the acid.
D) We need to know the initial concentration of the acid.
E) none of these
33. The pH of a 0.025 M weak acid solution is 5.29. Calculate K a
A) 1.0

10
–9
B) 5.1

10
–6
C) 1.5

10
–16
D) 2.0

10
–8
E) 2.0

10
–9
for this acid.
34. How many moles of benzoic acid, a monoprotic acid with K a
= 6.4

10
–5
, must be dissolved in 500. mL of
H
2
O to produce a solution with pH = 2.50?
A) 1.6

10
–1
B) 2.0

10
–2
C) 7.8

10
–2
D) 0.50
E) none of these
35. Calculate [H + ] in a 0.022 M solution of HCN, K a
A) 1.7

10
–4
M
= 6.2

10
–10
.
B) 3.7

10
–6
M
C) 2.7

10
–9
M
D) 6.2

10
–10
M
E) 5.5

10
–7
M
36. In a solution prepared by dissolving 0.100 mol of propionic acid in enough water to make 1.00 L of solution, the pH is observed to be 1.35. What is K a
A) 2.0

10
–2
B) 3.6

10
–2
C) 4.5

10
–2
D) 5.0

10
–12
for propionic acid (HC
3
H
5
O
2
)?
E) none of these
37. The pH of a 0.100 M solution of an aqueous weak acid (HA) is 3.20. What is K a
for the weak acid?
A) 6.3

10
–4
B) 7.2

10
–5
C) 4.0

10
–6
D) 3.2
E) none of these

38. The pH of a 0.21 M solution of a weak monoprotic acid, HA, is 2.66. Calculate K a
A) 2.1

10
–4
B) 2.2

10
–3
for this acid.
C) 4.8

10
–6
D) 2.3

10
–5
E) 4.6

10
–10
39. The pH of a solution made of 0.100 mol of a weak monoprotic acid HA in 1.000 L of solution is 1.470.
Calculate K a
for this acid.
A) 29.5
B) 0.0339
C) 0.0174
D) 0.100
E) 0
40. A 0.050 M aqueous solution of a weak monoprotic acid is 1.2% ionized at equilibrium at 25° C. Calculate K a for this acid.
A) 3.4

10
–2
B) 6.4

10
–8
C) 7.3

10
–33
D) 29
E) none of these
41. If an acid, HA, is 10.0% dissociated in a 1.0 M solution, what is K a
A) 9.1

10
–2
for this acid?
B) 1.1

10
–2
C) 8.1

10
–1
D) 6.3

10
–2
E) none of these
42. A 2.5 M solution of a weak acid is 0.52% ionized. What is K a
A) 6.8

10
–5
for this acid?
B) 1.1

10
–5
C) 0.11
D) 1.3

10
–2
E) none of these
43. Calculate the pH of a 0.10 M solution of HOCl, K a
= 3.5

10
–8
.
A) 4.23
B) 8.46
C) 3.73
D) 1.00
E) 3.23
44. Calculate the pOH of a 0.42 M solution of acetic acid ( K a
= 1.8

10
–5 ) at 25ºC.
A) 2.56
B) 9.26
C) 2.21
D) 11.44
E) 5.12
45. The p K a
of HOCl is 7.5. Calculate the pH of a 0.5 M solution of HOCl.
A) 7.5
B) 6.5
C) 3.9
D) 10.1
E) 0.3
46. How much water should be added to 10.0 mL of 12.0 M HCl so that it has the same pH as 0.90 M acetic acid
( K a
= 1.8

10
–5
)? (Assume the volumes are additive.)
A) 30 mL
B) 300 mL

C) 3 L
D) 30 L
E) 300 L
47. A 0.240 M solution of the salt NaA has pH = 8.40. Calculate K a
A) 6.60

10
–17
B) 1.05

10
–5
C) 3.80

10
–4
D) 2.63

10
–11
for the acid HA.
E) none of these
48. Calculate the pH of a solution made by a mixture of the following acids: 0.40 M HC
2
0.10 M HOCl ( K a
= 3.5

10
–8
), and 0.20 M HCN ( K a
= 6.2

10
–10
).
H
3
O
2
( K a
= 1.8

10
–5
),
A) 2.57
B) 3.49
C) 3.92
D) 4.23
E) 4.95
49. Calculate the pH of a 0.02 M solution of KOH.
A) 1.7
B) 2.0
C) 12.0
D) 12.3
E) We cannot calculate the answer unless a volume is given.
50. Which of the following aqueous solutions will have the highest pH?
For NH
3
, K b
= 1.8

10
–5
; for C
2
H
3
O
2
–
, K b
= 5.6

10
–10
.
A) 2.0 M NaOH
B) 2.0 M NH
3
C) 2.0 M HC
2
H
3
O
2
D) 2.0 M HCl
E) All these solutions will have the same pH.
51. Calculate the pOH of a 0.10 M solution of Ba(OH)
2
.
A) 13.30
B) 0.70
C) 1.00
D) 13.00
E) none of these
52. What is the equilibrium constant for the following reaction?
NH
4
+ + OH
–
NH
3
+ H
2
O
A)
B)
C)
D)
E)
K b

1
NH
3

K a

1
NH
4
+

K a

K w
NH
4
+

K b
K b

K w
NH
3


NH
3

K w

53. What is [OH
–
] in a 0.50 M pyridine (C
5
H
5
N; K b
= 1.7

10
–9
) solution?
A) 0.50 M
B) 2.9

10
–5
M
C) 1.8

10
–9
M
D) 3.3

10
–10
M
E) none of these
54. Calculate the pH of a 5.0 M solution of aniline (C
6
H
5
NH
2
; K b
= 3.8

10
–10
).
A) 4.36
B) 9.64
C) –0.070
D) 9.30
E) none of these
55. Calculate the percentage of pyridine (C
5 solution of pyridine ( K b
= 1.7

10
–9
).
H
5
N) that forms pyridinium ion, C
5
H
5
NH + , in a 0.10 M aqueous
A) 0.0060%
B) 1.6%
C) 0.77%
D) 0.060%
E) 0.013%
56. Calculate the pH of a 0.048 M solution of KOH.
A) 1.32
B) 2.68
C) 11.32
D) 12.68
E) none of these
57. A 2.00-g sample of NaOH( s ) is added to enough water to make 250.0 mL of solution at 25ºC. What is the pH of this solution?
A) 0.70
B) 14.90
C) 12.10
D) 13.30
E) 10.30
58. Calculate the pH of a solution made by mixing equal volumes of a solution of NaOH with a pH of 11.40 and a solution of KOH with a pH of 10.30. (Assume the volumes are additive.)
A) 1.10
B) 10.85
C) 11.13
D) 21.70
E) none of these
59. Calculate the pH of a solution that is 7.22

10
–4
M C
6
H
5
NH
2
. K b
is 3.8

10
–10
.
A) 7.50
B) 6.50
C) 6.28
D) 7.72
E) none of these
60. Calculate the pH of a 0.50 M NH
3
( K b
= 1.8

10
–5
) solution.
A) 13.72
B) 7.00
C) 4.78
D) 2.52
E) none of these
61. Consider two separate solutions of equal concentration. The first solution contains sodium hydroxide, and the second solution contains barium hydroxide. Which solution has the lower pH?
A) The sodium hydroxide solution.

B) The barium hydroxide solution.
C) The pH's of the two solutions are equal.
D) We need to know the concentrations to answer this question.
E) We need to know the volumes to answer this question.
62. The pH of a 2.1

10
–3
M solution of a weak base is 9.87. Calculate K b
for this base.
A) 1.2

10
–4
B) 6.4

10
–8
C) 2.6

10
–6
D) 8.7

10
–18
E) none of these
63. The pH of a 0.120 M solution of a weak base is 10.97 at 25ºC. Calculate the pH of a 0.0316 M solution of the base at 25ºC.
A) 2.89
B) 10.68
C) 10.39
D) 11.54
E) 3.32
64. The conjugate acid and conjugate base of bicarbonate ion, HCO
3
–
, are, respectively,
A) H
3
O + and OH
–
B) H
3
O +
C) H
2
and CO
CO
3
3
2–
and OH
–
D) H
2
CO
E) CO
3
2–
3
and CO
and OH
–
3
2–
65. If solid KCl is dissolved in pure water, will the solution be acidic, neutral, or basic?
A) acidic
B) neutral
C) basic
66. If solid NH
4
NO
3
is dissolved in pure water, will the solution be acidic, neutral, or basic?
A) acidic
B) neutral
C) basic
67. What is the pH of a 0.2 M solution of NH
4
Cl? K b
for NH
3
is 1.8

10
–5
.
A) 2.7
B) 5.0
C) 7.0
D) 9.0
E) 11.3
68. If solid NaCN is dissolved in pure water, will the solution be acidic, neutral, or basic?
A) acidic
B) neutral
C) basic
69. If solid NH
4
F is dissolved in pure water, will the solution be acidic, neutral, or basic?
For NH
3
, K b
= 1.8

10
–5
; for HF, K a
= 7.2

10
–4
.
A) acidic
B) neutral
C) basic

70. In which of the following are the species listed in order of increasing pH? ( K a
K a
for NH
4
+ is 5.56

10
–10
).
for HC
2
H
3
O
2
is 1.80

10
–5
, and
A) KCl, NH
4
Cl, HNO
3
, KOH, NaC
2
H
3
O
2
B) HNO
3
, KCl, NH
4
Cl, KOH, NaC
2
H
3
O
2
C) NH
4
Cl, HNO
3
, KCl, KOH, NaC
2
H
3
O
2
D) HNO
3
, NH
4
Cl, KCl, NaC
2
H
3
O
2
, KOH
E) none of these
Answer Key
1. A 11. B 21. E 31. A 41. B 51. B 61. A
2. E 12. B 22. B 32. C 42. A 52. A 62. C
3. C 13. A 23. C 33. A 43. A 53. B 63. B
4. D 14. C 24. B 34. C 44. D 54. B 64. D
5. C 15. C 25. A 35. B 45. C 55. E 65. B
6. C 16. B 26. C 36. B 46. D 56. D 66. A
7. D 17. D 27. D 37. C 47. C 57. D 67. B
8. A 18. C 28. B 38. D 48. A 58. C 68. C
9. D 19. C 29. A 39. C 49. D 59. D 69. A
10. A 20. B 30. A 40. E 50. A 60. E 70. D