This document contains 42 multiple choice questions about acid-base equilibria, weak acids, and acid-base buffers. The questions cover topics such as: the effect of adding salts on acid-base equilibria; calculating hydronium ion concentrations in solutions of weak acids; comparing percent dissociations of different weak acids; identifying the most basic solution among choices; buffer solutions; and calculating pH, pOH, and concentrations of species in various acid-base solutions.

1. Acid-Base Equilibrium
1. For the following reaction of hypochlorous acid (HOCl) with water,
HOCl + H2O <==> H3O+ + OCl-
what would be the effect of adding sodium hypochlorite (NaOCl) to the reaction at equilibrium?
a. The concentrations of both HOCl and H3O+ would increase.
b. The concentrations of both HOCl and H3O+ would decrease.
c. The concentration of HOCl would increase and the concentration of H3O+ would
decrease.
d. The concentration of HOCl would decrease and the concentration of H3O+ would
increase.
e. There would be no change because sodium hypochlorite is a salt without any
acidic or basic properties.
2. Calculate the molar hydronium ion concentration in a solution containing 0.23 M
hypochlorous acid (HOCl), a monoprotic weak acid used in bleach solutions. For HOCl,
Ka = 2.9 x 10-8.
3. Given three separate solutions containing equal concentrations of formic acid (Ka = 1.7 x
10-4), phenol (Ka = 1.3 x 10-10), and acetic acid (Ka = 1.8 x 10-5), select the response
below that has the acids arranged in order of increasing percent dissociation at
equilibrium.
a. formic < phenol < acetic
b. formic < acetic < phenol
c. acetic < formic < phenol
d. phenol < acetic < formic
e. No response is correct.
4. From the following choices, select the one that would be the most basic (least acidic).
a. 0.1 M hydrochloric acid (a strong acid)
b. 0.1 M acetic acid (a weak acid)
c. 0.1 M sodium acetate (the salt of a weak acid)
d. 0.1 M ammonium chloride (the salt of a weak base)
e. pure water
5. If 10 mL a 1.0 x 10-4 M solution of a strong acid were added to 100 mL each of one
solution containing 1.8 x 10-5 M hydrochloric acid and a second solution containing 1.0
M acetic acid (Ka = 1.8 x 10-5) plus 1.0 M sodium acetate, it is expected that the:
a. pH of both solutions would remain unchanged.
b. change in pH would be very large in both solutions.
c. change in pH would be the same in both solutions.

2. d. change in pH would be larger in the solution containing acetic acid and sodium
acetate.
e. change in pH would be larger in the HCl solution.
6. Addition of a strong acid to a solution of acetic acid at equilibrium (HOAc + H2O <=>
H3O+ + OAc-) would cause the:
a. acetate ion concentration to decrease.
b. acetate ion concentration to increase.
c. pH to increase.
d. hydroxide ion concentration to increase.
e. None of the above is correct.
7. Calculate to a first approximation the molar concentration of hydronium ion in a 0.171 M
solution of benzoic acid (HOBz, a monoprotic weak acid with Ka = 6.5 x 10-5).
8. Given that the acid dissociation constant for benzoic acid (HOBz) is Ka = 6.5 x 10-5,
calculate the basic dissociation constant, Kb , of the benzoate ion (OBz-).
9. Benzoic acid, C6H5CO2H, is a weak acid (Ka = 6.3 x 10-5). Calculate the initial
concentration (in M) of benzoic acid that is required to produce an aqueous solution of
benzoic acid that has a pH of 2.54.
10. Which of the following weak acid dissociation constants would result in the smallest
degree of dissociation?
a. Ka = 1.0 x 10-2
b. Ka = 1.0 x 10-3
c. Ka = 1.0 x 10-4
d. Ka = 1.0 x 10-5
11. Addition of sodium acetate to an acetic acid solution at equilibrium will cause:
a. no change in H3O+ concentration.
b. H3O+ concentration to decrease.
c. H3O+ concentration to increase.
d. concentrations of all species to increase.
e. a decrease in hydroxide concentrations.
12. What is the H3O+ concentration in a 0.17 M solution of a weak acid, HA, with a
dissociation constant of 3.21 x 10-6.
13. Calculate the hydronium ion concentration in a solution that contains 0.21 M acetic acid
and 0.17 M sodium acetate. For acetic acid, Ka = 1.8 x 10-5.
14. What is the concentration of the HPO4
2- ion in a 0.078 M solution of phosphoric acid
(H3PO4)? [Ka1 = 7.5 x 10-3; Ka2 = 6.3 x 10-8; Ka3 = 4.8 x 10-13]
15. Why is it necessary to take the acid-base properties of water into account when
computing the hydronium ion concentration of very dilute solutions of strong acids?
a. The hydroxide ion produced from the dissociation of water reacts with most of the
hydronium ion produced from the acid.
b. The dissociation constant for water is larger in dilute rather than in concentrated
solutions of acids.
c. The acids do not dissociate completely in dilute solutions.

3. d. The amount of hydronium ion produced by the dissociation of water is significant
compared to that produced by the acid.
e. The conjugate base of the strong acid reacts with the hydroxide ion produced
from the dissociation of water.
16. Hypochlorite ion (OCl-) is the conjugate base of hypochlorous acid (HOCl, Ka = 3.5 x 10-
8). What is the value of the base ionization equilibrium constant, Kb, for hypochlorite ion?
a. 3.5 x 10-22
b. 3.5 x 10-8
c. 2.9 x 10-7
d. 2.9 x 107
e. 4.7 x 109
17. Calculate the pH of an aqueous solution prepared to contain 1.3 x 10-3 M sodium nitrite
(NaNO2) if the acid dissociation equilibrium constant, Ka, for nitrous acid (HNO2) is 5.1
x 10-4.
a. 3.1
b. 5.1
c. 7.0
d. 7.3
e. 10.9
18. Calculate the carbonate ion concentration in a 0.10 M solution of the weak acid, carbonic
acid (H2CO3). The stepwise dissociation constants of carbonic acid are Ka1 = 4.5 x 10-7
and Ka2 = 4.7 x 10-11.
a. 4.7 x 10-11 M
b. 1.0 x 10-7 M
c. 4.5 x 10-7 M
d. 2.1 x 10-4 M
e. 3.5 x 10-3 M
19. The very first disinfectant used by Joseph Lister was called "carbolic acid". This
substance is now known as phenol (PhOH). What is the H3O+ ion concentration in a 0.10
M solution of phenol? [PhOH: Ka = 1.0 x 10-10]
a. 1.0 x 10-11
b. 3.2 x 10-5
c. 5.0 x 10-12
d. 3.2 x 10-6
20. The sweetener, saccharin, is a weak monoprotic acid with Ka = 2.1 x 10-12. Calculate the
H3O+ concentration in a solution that contains 1.0 x 10-2 mole of saccharin in 1.00 L of
otherwise pure water.
a. 1.4 x 10-7
b. 1.8 x 10-7
c. 2.1 x 10-12
d. 2.1 x 10-14

4. 21. When would the pH of a solution prepared by adding sodium formate to formic acid be
equal to the pKa of formic acid, HCO2H?
a. when [HCO2H] < [HCO2
-]
b. when [HCO2H] = [HCO2
-]
c. when [HCO2H] > [HCO2
-]
d. the pH of this buffer will never equal the pKa of formic acid.
22. Calculate the pH of a buffer prepared by mixing 0.10 mol of sodium formate and 0.05
mol of formic acid in 1.0 L of solution. [HCO2H: Ka = 1.8 x 10-4]
a. 1.8 x 10-4
b. 3.44
c. 4.05
d. 5.31
e. none of these
23. For a weak diprotic acid, H2A, for which Ka1 = 2.1 x 10-7 and Ka2 = 4.3 x 10-13, the A2-
ion concentration at equilibrium will be:
a. approximately equal to the initial concentration of H2A.
b. roughly equal to Ka2.
c. roughly equal to the HA- concentration.
d. much larger than the HA- concentration.
e. approximately equal to the H3O+ concentration.
24. Many insects discharge sprays containing weak acids as a means of defense. For
example, some ants discharge a spray that contains the weak acid, formic acid (HCO2H).
Calculate the pH of a 0.14 M solution of formic acid. Ka (HCO2H) = 1.8 x 10-4.
25. Calculate the pH of a solution prepared by dissolving 0.20 moles of benzoic acid
(abbreviated HOBz) and 0.15 moles of sodium benzoate (abbreviated NaOBz) in enough
water to make 1.0 L of solution. The acid-dissociation equilibrium constant for benzoic
acid is Ka = 6.3 x 10-5.
26. Consider an aqueous solution of a weak acid. Explain why the contribution of hydronium
ion from the dissociation of water (i.e., [H3O+]water) to the total hydronium ion
concentration is not equal to that for pure water (i.e., 1.0 x 10-7 M).
27. Calculate the [OH-] (in M) for an acetic acid solution (Ka = 1.8 x 10-5) having a pH of
6.32.
28. Ascorbic acid is also known as Vitamin C. In a 0.10 M solution of ascorbic acid 2.8% of
the ascorbic acid will dissociate. Consider the pH you would measure for a 0.25 M
solution of ascorbic acid. Which of the following statements is true?
a. The pH would show that the %-dissociation would be the same in both ascorbic
acid solutions.
b. The pH would show that the %-dissociation would be twice as much in the more
concentrated acid solutions.
c. The pH of the more concentrated solution would be lower.
d. You must know the Ka value for ascorbic acid before determining which of the
above selections is true.

5. 29. A buffer can be prepared by mixing:
a. a strong acid and its conjugate base.
b. a strong base and its conjugate acid.
c. a weak acid and its conjugate base.
d. a weak acid and a strong acid.
e. all responses above are correct.
30. Calculate the pH of a solution containing 0.1 M formic acid (a monoprotic weak acid
with Ka = 1.8 x 10-4 ) and 0.1 M sodium formate.
31. Calculate the molar hydronium ion concentration, [H3O+], in a 2.0 x 10-3 M solution of
hypoiodious acid (HOI, Ka = 2.3 x 10-11).
32. Calculate the hydroxide ion concentration, [OH-], in a 0.10 M solution of sodium
formate. (For the formate ion, OF-, Kb = 5.6 x 10-11.)
33. The dissociation constant for nitrous acid, HNO2, is Ka = 5.1 x 10-4. What is the
dissociation constant, Kb, for nitrite ion, NO2
-, the conjugate base of nitrous acid?
34. Which of the following solutions would be best to buffer a solution near pH = 4 ([H3O+]
= 1.0 x 10-4).
a. 1.0 x 10-4 M HCl
b. 1.0 x 10-4 M NaOH
c. A solution containing approximately equal concentrations of formic acid (Ka =
1.8 x 10-4) and sodium formate.
d. A solution containing approximately equal concentrations of hypochlorous acid
(HOCl, Ka = 2.9 x 10-8) and sodium hypochlorite (NaOCl).
e. A solution containing approximately equal concentrations of ammonia (Kb = 1.8 x
10-5) and ammonium chloride.
35. A 25.00 mL aliquot of a vinegar sample is diluted to 250.00 mL with water. Then a 25.00
mL aliquot of the diluted sample is titrated with strong base, requiring 22.13 mL of
0.1027 M sodium hydroxide to reach the endpoint. What is the molar concentration of
acid in the original vinegar sample before dilution?
36. Assume that a 25.00-mL aliquot of a solution containing a monoprotic weak acid is
titrated with a standard solution of sodium hydroxide, requiring 22.42 mL of titrant to
reach the end point. At which milliliter volume listed below will the pH be equal to the
pKa of the weak acid?
37. Which of the following solutions would be an acid/base buffer?
a. 0.1 M HCl, a strong acid
b. 0.1 M acetic acid, a weak acid
c. 0.1 M sodium acetate
d. 0.1 M acetic acid plus 0.1 M sodium acetate
e. pure water
38. Which of the following solutions would be the most basic?
a. 0.1 M HCl, a strong acid
b. 0.1 M acetic acid, a weak acid
c. 0.1 M sodium acetate

6. d. 0.1 M acetic acid plus 0.1 M sodium acetate
e. pure water
39. Calculate the hydronium ion concentration, [H3O+], in a 0.15 M solution of sodium
formate. For formic acid, Ka = 1.8 x 10-4.
40. In which of the following situations would the weak acid dissociate to the largest extent
(i. e., have the largest percent dissociation)?
a. 0.01 M formic acid, Ka = 1.8 x 10-4
b. 0.1 M formic acid, Ka = 1.8 x 10-4
c. 0.1 M acetic acid, Ka = 1.8 x 10-5
d. 0.01 M formic acid (Ka = 1.8 x 10-4) plus 0.15 M sodium formate
e. 1.0 x 10-4 M phenol, a monoprotic weak acid with Ka = 1.0 x 10-10
41. In which of the following solutions would the dissociation of water make the largest
contribution to the total hydronium ion concentration?
a. 0.01 M formic acid, Ka = 1.8 x 10-4
b. 0.1 M formic acid, Ka = 1.8 x 10-4
c. 0.1 M acetic acid, Ka = 1.8 x 10-5
d. 0.01 M formic acid (Ka = 1.8 x 10-4) plus 0.15 M sodium formate
e. 1.0 x 10-4 M phenol, a monoprotic weak acid with Ka = 1.0 x 10-10
42. A 25.0-mL aliquot of a monoprotic acid solution is diluted to 100 mL. Then a 25.0-mL
aliquot of this solution is titrated with a standard sodium hydroxide solution, requiring
17.1 mL of 0.107 M sodium hydroxide to reach the end point. What is the molar
concentration of the acid in the original solution?