1
General Chemistry II Jasperse
Acid-Base Chemistry. Extra Practice Problems
General Types/Groups of problems:
Conceptual Questions. Acids, Bases, and
Conjugates, Miscellaneous
p1
K
b
and pK
b
, Base Strength, and using K
b
or
pK
b
to Calculate [OH
-
], pOH, pH, and/or [H
+
]
p7-10
Recognizing Strong versus Weak Acids;
Recognizing Basic versus Nonbasic
p3
Recognizing Acid/Base Properties when
Ionics are Dissolved in Water
p11
pH Calculations; Relationships between pH and pOH
p4
Answers
p12
K
a
: Sense + Calculations. Using K
a
or pK
a
to Calculate
[H
+
] and/or pH; using pH to calculate K
a
or pK
a
p5
Conceptual Questions. Acids, Bases, and Conjugates, Miscellaneous
1. In the Brønsted–Lowry definition of acids and bases, an acid __________
a.
d.
breaks stable hydrogen bonds.
b.
e.
corrodes metals.
c.
2. In the Brønsted–Lowry definition of acids and bases, a base __________
a.
d.
breaks stable hydrogen bonds.
b.
e.
corrodes metals.
c.
3. In the following reaction in aqueous solution, the acid reactant is __________ and its conjugate base product is
__________.
CH
3
COOH + NH
3
CH
3
COO
–
+ NH
4
+
a.
d.
NH
3
; NH
4
+
b.
e.
CH
3
COOH; H
3
O
+
c.
4. In the following reaction in aqueous solution, the acid reactant is __________, and its conjugate base product is
__________.
CH
3
NH
2
+ HSO
4
–
CH
3
NH
3
+
+ SO
4
2–
a.
d.
HSO
4
–
; SO
4
2–
b.
e.
HSO
4
–
; H
3
O+
c.
5. Which of the following is the conjugate acid of the hydrogen phosphate ion, HPO
4
2–
?
a.
d.
PO
4
3–
b.
e.
H
3
O
+
c.
2
6. Which one of the following is not a conjugate acid–base pair?
a.
d.
HS
–
and H
2
S
b.
e.
NH
3
and NH
2
–
c.
7. Which one of the following is a conjugate acid–base pair?
a.
d.
H
2
O and O
2–
b.
e.
NaF and F
–
c.
8. Which one of the following is a conjugate acid–base pair?
a.
d.
NH
4
+
and NH
2
–
b.
e.
H
2
O and H
2
O
2
c.
9. Which one of the following is not a conjugate acid–base pair?
a.
d.
H
2
PO
4
–
and HPO
4
2–
b.
e.
H
2
O and OH
–
c.
10. The stronger the acid, __________
a.
d.
the less concentrated the conjugate base.
b.
e.
the more concentrated the conjugate base.
c.
11. Ammonia (NH
3
) acts as a weak base in aqueous solution. What is the acid that reacts with this base when ammonia is
dissolved in water?
a.
none, there are no acids in pure water
b.
H
2
O
c.
NH
4
+
d.
trick question, because no acids are present, ammonia cannot act as a base
e.
oxygen that always is dissolved in water
12. The base ionization constant K
b
describes which of the following reactions for a weak base, B, in aqueous solution?
(Note: often the base will be anionic rather than neutral, but “B” here is meant to represent anionic or neutral bases,
which will gain one H and become one charge unit more positive whether starting neutral or anionic.)
a.
d.
B + OH
–
BH
–
+ O
2–
b.
e.
BH
+
+ OH
–
B + H
2
O
c.
3
Recognizing Strong versus Weak Acids; Recognizing Basic versus Nonbasic
13. Which of the following is a strong acid?
a.
d.
HCO
3
–
b.
e.
HOCl
c.
14. Which one of the following is a strong acid?
a.
d.
hydrofluoric acid, HF
b.
e.
perchloric acid, HClO
4
c.
15. Which one of the following is not a strong acid?
a.
d.
hydrochloric acid, HCl
b.
e.
perchloric acid, HClO
4
c.
16. Which of the following compounds cannot be a Brønsted–Lowry base?
a.
d.
NH
4
+
b.
e.
SH
–
c.
17. Each of the following pairs contains one strong acid and one weak acid EXCEPT:
a.
H
2
SO
4
and H
2
CO
3
b.
HNO
3
and HNO
2
c.
HBr and H
3
PO
2
d.
HSO
4
-
and HCN
e.
HCl and H
2
S
18. Which one of the following is NOT basic?
a.
d.
SO
4
2-
b.
e.
HPO
4
2-
c.
19. Which one of the following is basic?
a.
d.
HSO
4
-
b.
e.
SO
4
2-
c.
4
pH Calculations; Relationships between pH and pOH
20. If the pH of a solution increases by 2 units (e.g., from 1 to 3), then the ratio of the new to the original hydronium ion
concentration is __________
a.
d.
1/100.
b.
e.
1/1, unchanged
c.
21. When [H
+
] = 1.0 × 10
–7
M in water at 25°C, then __________
a.
d.
[OH
–
] = 1.0 × 10
7
M.
b.
e.
[OH
–
] = 0 M.
c.
22. When [H
+
] = 4.0 × 10
–9
M in water at 25°C, then __________
a.
d.
pH = 8.40.
b.
e.
pH = –9.40
c.
23. A solution with pH of 9.50 has a pOH of __________
a.
d.
23.5.
b.
e.
19.0.
c.
24. A solution with an [OH
–
] concentration of 1.20 × 10
–7
M has a pOH and pH of __________
a.
d.
7.08 and 6.92
b.
e.
5.94 and 8.06
c.
25. A solution with a pOH of 4.3 has a [H
+
] of __________
a.
d.
2.0 × 10
–10
M.
b.
e.
4.3 M.
c.
26. Which statement, A–D, is not correct? If all are correct, respond E. Pure water at 25°C has __________
a.
d.
pH = 7.
b.
e.
A–D are all correct.
c.
5
K
a
: Sense + Calculations. Using K
a
or pK
a
to Calculate [H
+
] and/or pH; using pH to calculate K
a
or pK
a
27. Solutions of each of the hypothetical acids in the following table are prepared with an initial concentration of 0.100 M.
Which of the four solutions will have the lowest pH and be most acidic?
Acid
pK
a
HA
4.00
HB
7.00
HC
10.00
HD
11.00
a.
HA
d.
HD
b.
HB
e.
All will have the same pH because the concentrations are the same.
c.
HC
28. What is the hydronium ion concentration of a 0.010 M solution of acetic acid? K
a
for acetic acid is 1.8 x 10
–5
a.
d.
1.8 × 10
–7
b.
e.
4.2 × 10
–4
c.
29. What is the pH of a 0.010 M solution of acetic acid? K
a
for acetic acid is 1.8 × 10
–5
a.
d.
3.37
b.
e.
6.74
c.
30. When values of K
a
are small (e.g., 1 × 10
–5
) and concentrations of weak acids [HA] are relatively large (e.g., 0.10 M),
and assuming there is no other source of anion A
–
, the hydronium ion concentration of the solution can be calculated
using which expression?
a.
d.
[H
+
] = K
a
K
b
[HA]
b.
e.
[H
+
] = K
a
[HA]
2
/[A
–
]
c.
31. The first disinfectant used by Joseph Lister was called carbolic acid. This substance now is known as phenol, C
6
H
5
OH
(pK
a
= 10.0). What is the pH of a 0.10 M solution of phenol?
a.
d.
5.5
b.
e.
4.5
c.
32. The pH of a popular soft drink is 3.4; what is its hydronium ion concentration?
a.
d.
1.0 × 10
–7
M
b.
e.
5.0 × 10
–5
M
c.
6
33. The concentration of acetic acid (pK
a
= 4.75) in vinegar is about 1.0 M. With this information, what do you predict the
pH of vinegar to be?
a.
d.
7.0
b.
e.
5.35
c.
34. Boric acid frequently is used as an eyewash to treat eye infections. The pH of a 0.050 M solution of boric acid is 5.28.
What is the value of the boric acid ionization constant, Ka?
a.
d.
5.79 × 10
–4
b.
e.
5.33 × 10
–12
c.
35. A 0.100 M solution of a monoprotic weak acid has a pH of 3.00. What is the pK
a
of this acid?
a.
d.
9.99
b.
e.
6.00
c.
36. The acidic ingredient in vinegar is acetic acid. The pH of vinegar is around 2.4, and the molar concentration of acetic
acid in vinegar is around 0.85 M. Based on this information, determine the value of the acid ionization constant, K
a
, for
acetic acid.
a.
d.
1.9 × 10
–5
b.
e.
7.4 × 10
–3
c.
37. Three acids found in foods are lactic acid (in milk products), oxalic acid (in rhubarb), and malic acid (in apples). The
pK
a
values are LA = 3.88, OA = 1.23, and MA = 3.40. Which list has these acids in order of decreasing acid strength?
a.
d.
OA > LA > MA
b.
e.
MA > LA > OA
c.
38. Use the following acid ionization constants to identify the correct decreasing order of base strengths.
HF
K
a
= 7.2 × 10
–4
HNO
2
K
a
= 4.5 × 10
–4
HCN
K
a
= 6.2 × 10
–10
a.
d.
F
–
> NO
2
–
> CN
–
b.
e.
NO
2
–
> CN
–
> F
–
c.
7
K
b
and pK
b
, Base Strength, and using K
b
or pK
b
to Calculate [OH
-
], pOH, pH, and/or [H
+
]
39. A cup of coffee has a hydroxide ion concentration of 1.0 × 10
–10
M. What is the pH of this coffee?
a.
d.
7
b.
e.
–10
c.
40. What is the concentration of [OH
–
] in a 0.20 M solution of ammonia? The K
b
value for ammonia is 1.8 × 10
–5
.
a.
d.
1.9 × 10
–3
M
b.
e.
4.2 × 10
–4
M
c.
41. What is the pOH of a 0.20 M solution of ammonia? The K
b
value for ammonia is 1.8 × 10
–5
a.
d.
2.72
b.
e.
3.38
c.
42. What is the pH of a 0.20 M solution of ammonia? The K
b
value for ammonia is 1.8 × 10
–5
a.
d.
11.28
b.
e.
2.72
c.
43. What is the hydronium ion concentration of a 0.20 M solution of ammonia? The K
b
value for ammonia is 1.8 × 10
–5
a.
d.
5.2 × 10
–12
b.
e.
1.9 × 10
–3
c.
44. What is the pH of a 0.500 M solution of trimethylamine (pK
b
= 4.13)?
a.
d.
4.42
b.
e.
5.91
c.
8
Miscellaneous problems involving Weak Bases and perhaps their Conjugates.
45. Phosphoric acid is a triprotic acid, ionizing in the following sequential steps:
H
3
PO
4
+ H
2
O H
2
PO
4
–
+ H
3
O
+
K
a
H
2
PO
4
–
+ H
2
O HPO
4
2–
+ H
3
O
+
K
a
HPO
4
2–
+ H
2
O PO
4
3–
+ H
3
O
+
K
a
Write the K
b
expression for the base, sodium phosphate (Na
3
PO
4
)?
46. Phosphoric acid is a triprotic acid, ionizing in the following sequential steps:
H
3
PO
4
+ H
2
O H
2
PO
4
–
+ H
3
O
+
H
2
PO
4
–
+ H
2
O HPO
4
2–
+ H
3
O
+
HPO
4
2–
+ H
2
O PO
4
3–
+ H
3
O
+
Write the K
b
expression for the base, sodium dihydrogen phosphate (NaH
2
PO
4
)?
47. Use the following acid ionization constants to identify the correct decreasing order of base strengths.
HF
K
a
= 7.2 × 10
–4
HNO
2
K
a
= 4.5 × 10
–4
HCN
K
a
= 6.2 × 10
–10
a.
d.
F
–
> NO
2
–
> CN
–
b.
e.
NO
2
–
> CN
–
> F
–
c.
48. Three acids found in foods are lactic acid (in milk products), oxalic acid (in rhubarb), and malic acid (in apples). The
pK
a
values are LA = 3.88, OA = 1.23, and MA = 3.40. Which list has the conjugate bases of these acids in order of
decreasing strength?
a.
d.
oxalate > lactate > malate
b.
e.
malate > lactate > oxalate
c.
49. What is the pH of a 0.20 M solution of cubaramine? The K
b
value for jaspersamine is 2.5 × 10
–6
.
50. What is the pH of a 0.10 M solution of trimethylamine (pK
b
= 4.13)?
9
51. How would you calculate K
b
for the formate ion, given that the K
a
for formic acid is 1.8 × 10
–4
? (K
w
=1.0× 10
–14
)
a.
d.
K
b
= K
w
+ K
a
b.
e.
K
b
= K
w
– K
a
c.
52. What is the pH of a 0.20 M solution of jaspersamine? The pK
b
value for jaspersamine 4.40.
53. What is the pH of a 0.15 M solution of weak acid ammonium bromide? The K
b
value for ammonia is 1.8 × 10
–5
.
a.
d.
5.04
b.
e.
10.08
c.
54. Phosphoric acid is a triprotic acid, ionizing in the following sequential steps:
H
3
PO
4
+ H
2
O H
2
PO
4
–
+ H
3
O
+
H
2
PO
4
–
+ H
2
O HPO
4
2–
+ H
3
O
+
HPO
4
2–
+ H
2
O PO
4
3–
+ H
3
O
+
Which equilibrium is most important in determining the pH of a solution of sodium phosphate?
a.
d.
H
2
PO
4
–
+ H
2
O H
3
PO
4
+ OH
–
b.
e.
2H
2
O H
3
O
+
+ OH
–
c.
55. Solutions of sodium salts of the acids in the following table are prepared with an initial concentration of 0.500 M.
Which solution will have the highest pH and be the most basic?
Acid
pK
a
HA
4.00
HB
7.00
HC
10.00
HD
11.00
a.
NaA
b.
NaB
c.
NaC
d.
NaD
e.
All will have the same pH because the concentrations are the same.
10
Getting Information about an Acid or Base Based on K
a
or pK
a
or K
b
or pK
b
of the conjugate.
56. What is the pH of a 0.20 M solution of sodium acetate? The K
a
for acetic acid is 1.8 x 10
–5
?
57. What is the pH of a 0.40 M solution of sodium nitrite, NaNO
2
? The pK
a
for nitrous acid (HNO
2
) is 3.35.
58. What is the pH of a 0.20 M solution of weak acid jaspersammonium bromide? The K
b
value for jaspersamine is 4.0 ×
10
–5
.
59. What is the pH of a 0.10 M solution of weak acid trimethylammonium chloride? The pK
b
= 4.13 for it’s conjugate
base triethylamine
11
Recognizing Acid/Base Properties when Ionics are Dissolved in Water
60. Aqueous solutions of __________ are basic.
a.
d.
NaI
b.
e.
KI
c.
61. Which one of the following salts forms aqueous solutions with pH = 7?
a.
d.
NaNO
2
b.
e.
Na
2
CO
3
c.
62. Which one of the following salts forms aqueous solutions with pH = 7?
a.
d.
NaH
2
PO
4
b.
e.
Na
2
CO
3
c.
63. Which one of the following salts does not produce a basic solution when dissolved in water?
a.
d.
NaNO
b.
e.
NaHCO
3
c.
64. The pH of an aqueous sodium fluoride (NaF) solution is __________ because __________
a.
7; sodium fluoride is a simple salt.
b.
above 7; fluoride is a weak base.
c.
below 7; fluoride reacts with water to make hydrofluoric acid.
d.
about 7; fluoride is a weak base, but produces hydrofluoric acid, and these two neutralize one
another.
e.
0; sodium fluoride is a salt not an acid or a base.
65. Which one of the following, A–D, is correct? If all are correct, respond E.
a.
d.
Na
2
HPO
4
is a weaker base than NaH
2
PO
4
.
b.
e.
All of these statements are correct.
c.
66. Which of the following groups, A–D, consist of salts that all form basic solutions in water? (Ac = acetate) If none or
all satisfy this criterion, respond E.
a.
d.
NaHCO
3
, NaF, NH
4
Cl, Na
2
SO
3
b.
e.
None or all of the above.
c.
12
General Chemistry II Jasperse ANSWERS
Acid-Base Chemistry. Extra Practice Problems
1. A
2. B
3. A
4. D
5. B
6. B
7. A
8. C
9. B
10. B
11. B
12. C
13. A
14. E
15. C
16. D
17. D
18. B
19. E
20. D
21. C
22. D
23. C
24. A
25. D
26. E
27. A
28. E
29. D
30. C
31. D
32. B
33. B
34. B
35. A
36. D
37. C
38. A
39. B
40. D
41. D
42. D
43. D
44. B
45. K
b
=([HPO
4
2-
][HO
-
])/[PO
4
3-
]
46. K
b
=([H
3
PO
4
][HO
-
])/[H
2
PO
4
-
]
47. A
48. C
49. pH=10.85
50. pH=11.44
51. B
52. pH=11.45
53. D
54. C
55. D
56. pH = 9.02
57. pH = 8.48
58. pH = 5.15
59. pH = 5.44
60. A
61. B
62. C
63. B
64. B
65. A
66. C