MSC: Quantitative
61. A 75.0-mL sample of 0.0500 M HCN (Ka = 6.2 10–10) is titrated with 0.277 M NaOH.
What is the [H+] in the solution after 3.0 mL of 0.277 M NaOH have been added?
A)
4.6 10–6 M
B)
1.0 10–7 M
C)
3.5 M
D)
2.2 10–9 M
E)
none of these
62. A student titrates an unknown weak acid, HA, to a pale pink phenolphthalein endpoint with
25.0 mL of 0.100 M NaOH. The student then adds 13.0 mL of 0.100 M HCl. The pH of the
resulting solution is 4.7. Which of the following is true?
A)
At pH 4.7, half the conjugate base, A–, has been converted to HA.
B)
The pKa of the acid is 4.7.
C)
The pKa of the acid is less than 4.7.
D)
The pKa of the acid is greater than 4.7.
E)
More than one of the above is correct.
63. How many moles of HCl(g) must be added to 1.0 L of 2.4 M NaOH to achieve a pH of
0.00? (Neglect any volume change.)
A)
1.4 moles
B)
4.4 moles
C)
3.4 moles
D)
5.4 moles
E)
none of these
64. A 50.0-mL sample of a 1.50 M NaOH solution is titrated with a 1.86 M HCl solution. What
will be the final volume of solution when the NaOH has been completely neutralized by the
HCl?
A)
90.3 mL
B)
40.3 mL
C)
75.3 mL
D)
190. mL
E)
94.3 mL
65. You have 75.0 mL of 0.11 M HA. After adding 30.0 mL of 0.10 M NaOH, the pH is 5.50.
What is the Ka value of HA?
A)
3.2 10–6
B)
1.8 10–6
C)
0.57
D)
1.1 10–6
E)
none of these
66. Consider the titration of 100.0 mL of 0.10 M H2A (Ka1 = 1.50 10–4; Ka2 = 3.89 10–7) with
0.20 M NaOH. Calculate the [H+] after 75.0 mL of 0.20 M NaOH has been added.
A)
7.8 10–7 M
B)
2.6 10–8 M
C)
1.9 10–7 M
D)
3.9 10–7 M
E)
none of these
67. Consider the titration of 100.0 mL of 0.10 M H2A (Ka1 = 1.5 10–4; Ka2 = 8.0 10–7) with
0.20 M NaOH. Calculate the volume of 0.20 M NaOH required to reach an [H+] of 6.0 10–
4 M.
A)
0 mL
B)
10. mL
C)
25. mL
D)
50. mL
E)
65. mL
68. A 50.00-mL sample of a 1.00 M solution of the diprotic acid H2A (Ka1 = 1.0 10–6 and
Ka2 = 1.0 10–10) is titrated with 2.00 M NaOH. How many mL of 2.00 M NaOH must be
added to reach a pH of 10?
A)
0 mL
B)
12.5 mL
C)
25.0 mL
D)
37.5 mL
E)
none of these
69. Consider the titration of 100.0 mL of 0.100 M H2A (Ka1 = 1.50 10–4; Ka2 = 1.00 10–8).
How many milliliters of 0.100 M NaOH must be added to reach a pH of 5.000?
A)
41.9 mL
B)
93.8 mL
C)
100. mL
D)
200. mL
E)
60.0 mL
70. A 100.0-mL sample of 0.503 M H2A (diprotic acid) is titrated with 0.200 M NaOH. After
125.0 mL of 0.200 M NaOH has been added, the pH of the solution is 4.50. Calculate Ka1
for H2A.
A)
3.2 10–10
B)
4.5
C)
3.1 10–5
D)
not enough information to calculate
E)
none of these
Consider the following information about the diprotic acid, ascorbic acid. (H2As for short,
molar mass 176.1)
H2As HAs– + H+ pKa = 4.10 (Ka = 7.9 10–5)
HAs– As2– + H+ pKa = 11.79 (Ka = 1.6 10–12)
The titration curve for disodium ascorbate, Na2As, with standard HCl is shown below:
71. What major species is (are) present at point III?
A)
As2– and HAs–
B)
HAs– only
C)
HAs– and H2As
D)
H2As only
E)
H2As and H+
72. What is the pH at point I (V1/2 HCl added)?
A)
4.10
B)
7.95
C)
11.79
D)
12.39
E)
none of these
73. What is the pH at point III?
A)
4.10
B)
7.95
C)
11.79
D)
12.39
E)
none of these
74. Which of the following is a major species present at point IV?
A)
H2As
B)
HAs–
C)
As2–
D)
H+
E)
none of these
75. A solution contains 10. mmol of H3PO4 and 5.0 mmol of NaH2PO4. How many milliliters of
0.10 M NaOH must be added to reach the second equivalence point of the titration of the
H3PO4 with NaOH?
A)
250
B)
150
C)
1.0 102
D)
50
E)
2.0 102
76. A solution contains 25 mmol of H3PO4 and 10. mmol of NaH2PO4. What volume of 2.0 M
NaOH must be added to reach the second equivalence point of the titration of the H3PO4
with NaOH?
A)
5.0 mL
B)
12 mL
C)
25 mL
D)
30. mL
E)
60. mL
77. A 100.-mL sample of a 0.10 M solution of H3PO4 is titrated with 0.20 M NaOH. What
volume of base must be added to reach the third equivalence point?
A)
50. mL
B)
1.0 102
C)
150 mL
D)
2.0 102
E)
250 mL
78. For carbonic acid (H2CO3), Ka1 = 4.30 10–7 and Ka2 = 5.62 10–11. Calculate the pH of a
0.56 M solution of Na2CO3.
A)
2.00
B)
10.06
C)
3.94
D)
12.00
E)
9.00
79. A solution containing 10. mmol of and 5.0 mmol of is titrated with 1.8 M HCl.
What volume of HCl must be added to reach the first equivalence point?
A)
2.8 mL
B)
5.6 mL
C)
10.6 mL
D)
15.6 mL
E)
20.6 mL
80. A solution containing 10. mmol of and 5.0 mmol of is titrated with 1.7 M HCl.
What total volume of HCl must be added to reach the second equivalence point?
A)
8.8 mL
B)
5.9 mL
C)
2.9 mL
D)
14.7 mL
E)
19.7 mL
81. You dissolve 1.15 grams of an unknown diprotic acid in 200.0 mL of H2O. This solution is
just neutralized by 5.00 mL of a 1.00 M NaOH solution. What is the molar mass of the
unknown acid?
A)
230
B)
115
C)
28.8
D)
460
E)
none of these
82. A 2.36-g sample of an acid, H2X, requires 45.0 mL of a 0.500 M NaOH solution for
complete reaction (removing both protons). The molar mass of the acid is:
A)
105
B)
255
C)
232
D)
210
E)
none of these
83. A 0.210-g sample of an acid (molar mass = 192 g/mol) is titrated with [$X] mL of [$Y] M
NaOH to a phenolphthalein endpoint. The formula of the acid is:
A)
HA
B)
H2A
C)
H3A
D)
H4A
E)
not enough information given
84. Consider the titration of 100.0 mL of 0.250 M aniline (Kb = 3.82 10–10) with 0.500 M
HCl. Calculate the pH of the solution at the stoichiometric point.
A)
5.10
B)
9.42
C)
2.68
D)
11.32
E)
none of these
85. Consider the titration of 100.0 mL of 0.250 M aniline (Kb = 3.8 10–10) with 0.500 M HCl.
For calculating the volume of HCl required to reach a pH of 8.0, which of the following
expressions is correct? (x = volume in mL of HCl required to reach a pH of 8.0)
A)
= [aniline]
B)
[H+] = x
C)
= [aniline]
D)
= [aniline]
E)
none of these
86. A 100.0-mL sample of 0.2 M (CH3)3N (Kb = 5.33 10–5) is titrated with 0.2 M HCl. What is
the pH at the equivalence point?
A)
2.6
B)
8.6
C)
10.7
D)
5.4
E)
7.0
87. Calculate the pH at the equivalence point for the titration of 1.0 M ethylamine, C2H5NH2, by
1.0 M perchloric acid, HClO4. (pKb for C2H5NH2 = 3.25)
A)
6.05
B)
2.24
C)
5.53
D)
2.09
E)
5.38
88. What volume of 0.0100 M NaOH must be added to 1.00 L of 0.0500 M HOCl to achieve a
pH of 8.00? The Ka for HOCl is 3.5 10–8.
A)
1.0 L
B)
5.0 L
C)
1.2 L
D)
3.9 L
E)
none of these
89. Which of the following is the net ionic equation for the reaction that occurs during the
titration of nitric acid with potassium hydroxide?
A)
HNO3 + K+ OH– → KNO3 + H2O
B)
HNO3 + H2O → NO3– + H3O+
C)
HNO3 + KOH → K+ + NO3– + H2O
D)
HNO3 + OH– → NO3– + H2O
E)
H+ + OH– → H2O
90. In titrating 100 mL of 0.10 M HCl (aq) with 0.10 M NaOH, the pH does not change a great
deal initially. Why is this?
A)
The amount of OH– has no affect on the pH of aqueous solutions.
B)
The H+ from the HCl (aq) acts like a buffer.
C)
The major species when the acid and base are mixed form a buffered solution.
D)
The statement “In titrating 100 mL of 0.10 M HCl (aq) with 0.10 M NaOH, the pH
does not change a great deal initially.” is not true.
E)
None of these.
91. You have 100.0 mL of 0.100 M aqueous solutions of each of the following acids: HCN, HF,
HCl, and HC2H3O2. You titrate each with 0.100 M NaOH (aq). Rank the pHs of each of the
solutions when each are titrated to the equivalence point, from highest to lowest pH.
Ka for HCN = 6.2 10–10
Ka for HF = 7.2 10–4
Ka for HC2H3O2 = 1.8 10–5
A)
HCN, HC2H3O2, HF, HCl
B)
HCl, HF, HCN, HC2H3O2
C)
HF, HCN, HC2H3O2, HCl
D)
HC2H3O2, HCl, HCN, HF
E)
none of these
92. How many of the following will raise the pH of a weak acid HA in aqueous solution?
I.
addition of water
II.
making a buffered solution by adding NaA(s)
III.
addition of NaCl(s)
IV.
addition of HNO3
V.
titrating with KOH
A)
1
B)
2
C)
3
D)
4
E)
5
93. A 25.00-mL sample of propanoic acid, CH3CH2COOH, of unknown concentration was
titrated with 0.111 M KOH. The equivalence point was reached when 44.54 mL of base had
been added.What is the concentration of the propanoate ion at the equivalence point?
A)
0.111 M
B)
0.0711 M
C)
0.198 M
D)
0.128 M
E)
0.147 M
94. A 50.00-mL solution of 0.0350 M hydrocyanic acid (Ka = 6.2 10–10) is titrated with a
0.0333 M solution of sodium hydroxide as the titrant. What is the pH of the acid solution
after 15.00 mL of titrant have been added? (Kw = 1.00 10–14)
A)
1.46
B)
5.33
C)
8.81
D)
10.60
E)
9.21
95. A 50.00-mL solution of 0.0304 M ethanolamine (Kb = 3.2 10–5) is titrated with a 0.0282 M
solution of hydrochloric acid as the titrant. What is the pH of the base solution after
23.24 mL of titrant have been added? (Kw = 1.00 10–14)
A)
10.99
B)
12.48
C)
4.49
D)
9.62
E)
4.38
96. A 50.00-mL solution of 0.0217 M butyric acid (Ka = 1.5 10–5) is titrated with a 0.0302 M
solution of sodium hydroxide as the titrant. What is the pH of at the equivalence point?
(Kw = 1.00 10–14)
A)
8.46
B)
5.54
C)
4.82
D)
10.64
E)
9.18
97. A 50.00-mL solution of 0.0350 M aniline (Kb = 3.8 10–10) is titrated with a 0.0127 M
solution of hydrochloric acid as the titrant. What is the pH at the equivalence point?
(Kw = 1.0 10–14)
A)
4.58
B)
10.69
C)
5.73
D)
9.42
E)
3.31
Consider the titration of 100.0 mL of the weak diprotic acid H2A (0.10 M) with 0.20 M
NaOH. What are the major species at each of the following points in the titration? (Water is
always assumed to be a major species.)
98. Before any NaOH is added
A)
HA–
B)
H2A, HA–
C)
HA–, A2–
D)
H2A
E)
none of these
99. After 25.0 mL of 0.20 M NaOH is added
A)
HA–
B)
H2A, HA–
C)
HA–, A2–
D)
H2A
E)
none of these
100. After 50.0 mL of 0.20 M NaOH is added
A)
HA–
B)
H2A, HA–
C)
HA–, A2–
D)
H2A
E)
none of these
101. After 75.0 mL of 0.20 M NaOH is added
A)
HA–
B)
H2A, HA–
C)
HA–, A2–
D)
H2A
E)
none of these
102. After 200.0 mL of 0.20 M NaOH is added
A)
HA–
B)
H2A, HA–
C)
HA–, A2–
D)
H2A
E)
none of these
103. Consider the following indicators and their pH ranges:
Methyl orange
3.2-4.4
Methyl red
4.8-6.0
Bromothymol blue
6.0-7.6
Phenolphthalein
8.2-10.0
Alizarin yellow
10.1-12.0
Assume an indicator works best when the equivalence point of a titration comes in the
middle of the indicator range. For which of the following titrations would methyl red be the
best indicator?
A)
0.100 M HNO3 + 0.100 M KOH
B)
0.100 M aniline (Kb = 3.8 10–10) + 0.100 M HCl
C)
0.100 M NH3 (Kb = 1.8 10–5) + 0.100 M HCl
D)
0.100 M HF (Ka = 7.2 10–4) + 0.100 M NaOH
E)
0.100 M acetic acid (Ka = 1.8 10–5) + 0.100 M NaOH
104. Assume an indicator works best when the equivalence point of a titration comes in the
middle of the indicator range. Which indicator would be best for the following titration?
0.100 M HOCl (Ka = 3.5 10–8) + 0.100 M NaOH
A)
crystal violet (0.2 – 1.8)
B)
phenolphthalien (8.2 – 10.0)
C)
methyl orange (3.2 – 4.4)
D)
thymolphthalein (9.5 – 10.5)
E)
cresol red (7.0 – 8.8)
105. In the titration of a weak acid HA with 0.100 M NaOH, the stoichiometric point is known to
occur at a pH value of approximately 10. Which of the following indicator acids would be
best to use to mark the endpoint of this titration?
A)
indicator A, Ka = 10–14
B)
indicator B, Ka = 10–11
C)
indicator C, Ka = 10–8
D)
indicator D, Ka = 10–6
E)
none of these
106. In the titration of a weak acid, HA, with a sodium hydroxide solution of approximately the
same concentration, the stoichiometric point occurs at pH = 9.5. Which of the following
weak acid indicators would be best suited to mark the endpoint of this titration?
A)
indicator A, Ka = 10–11
B)
indicator B, Ka = 10–13
C)
indicator C, Ka = 10–9
D)
indicator D, Ka = 10–7
E)
indicator E, Ka = 10–5
107. In the titration of a weak acid HA with 0.100 M NaOH, the stoichiometric point is known to
occur at a pH value of approximately 11. Which of the following indicators would be best to
use to mark the endpoint of this titration?
A)
an indicator with Ka = 10–10
B)
an indicator with Ka = 10–8
C)
an indicator with Ka = 10–14
D)
an indicator with Ka = 10–11
E)
an indicator with Ka = 10–12
108. A certain indicator HIn has a pKa of 9.00 and a color change becomes visible when 7.00%
of it is In–. At what pH is this color change visible?
A)
10.2
B)
3.85
C)
6.15
D)
7.88
E)
none of these
109. Methyl orange is an indicator with a Ka of 1 10–4. Its acid form, HIn, is red, while its base
form, In–, is yellow. At pH 6.0, the indicator will be
A)
red
B)
orange
C)
yellow
D)
blue
E)
not enough information