Acids-Bases Equilibria
AP Chemistry
Acids-Bases Equilibria Practice Problems
1) The concentration of H+ in a 1.0 M HF solution is 7.2 x 10-4M, and the percent
dissociation of HF is 2.7%. Calculate [H+] and the percent dissociation of HF in a
solution containing 1.0M HF (Ka = 7.2 x 10-4) and 1.0 M NaF
2)
a. Calculate the pH of a 0.100 M propanoic acid (HC3H5O2) and a mixture
containing 0.100 M of the acid and 0.100 M NaC3H5O2. Ka for the acid is 1.3 x
10-5.
b. Compare the percent dissociation of the acids in part 2a and explain the large
difference in percent dissociation of the acid.
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Acids-Bases Equilibria
AP Chemistry
3) A buffered solution contains 0.50 M acetic acid (Ka = 1.8 x 10-5) and 0.50 M sodium
acetate. Calculate the pH of this solution.
4) Calculate the change in pH that occurs when 0.0100 mol solid sodium hydroxide is added
to a 1.0 L of buffered solution described in question 3. Compare this pH range with that
which occurs when 0.010 mol solid sodium hydroxide is added to 1.0 L water.
5) Calculate the pH of a solution containing 0.75 M lactic acid (Ka = 1.4 x 10-4) and 0.25 M
sodium lactate. Lactic acid (HC3H5O3) is a common constituent of biological systems.
For example, it is found in milk and is present in human muscle tissue during exertion.
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Acids-Bases Equilibria
AP Chemistry
6) A buffered solution contains 0.25 M ammonia (Kb = 1.8 x 10-5) and 0.40 M NH4Cl.
Calculate the pH of this solution.
7) Calculate the pH of the solution that results when 0.10 mol gaseous HCl is added to 1.0 L
of the buffer system in question #6.
8) Calculate the correct volumes of the 0.1 M acetic acid solution and the 0.1 M sodium
acetate solution needed to make 50 mL of a buffer solution with a pH value of 5.00. The
Ka of acetic is 1.8 x 10-5.
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Acids-Bases Equilibria
AP Chemistry
9) Calculate the change in pH that occurs when 0.010 mol gaseous HCl is added to 1.0 L of
each of the following solutions, Ka = 1.8 x 10-5.
a. Solution A: 5.00 M acetic acid / 5.00 M sodium acetate
b. Solution B: 0.050 M acetic acid / 0.050 sodium acetate
10) A chemist needs a solution buffered at a pH of 4.30 and can choose from the following
acid/sodium salt pairs:
a. Chloroacetic acid, Ka = 1.35 x 10-3
b. Propanoic acid, Ka = 1.3 x 10-5
c. Benzoic acid, Ka = 6.4 x 10-5
d. Hypochlorous acid, Ka = 3.5 x 10-8
Calculate the ratio of ([HA] / [A-]) required for each system to yield a pH of 4.30. Which
system works best?
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Acids-Bases Equilibria
AP Chemistry
11) A strong acid-strong base titration is conducted. 50.0 mL of 0.200 M HNO 3 and 0.100 M
NaOH is used. Calculate the pH of the solution at the following points:
a. Before NaOH has been added
b. 10.0 mL of NaOH is added
c. 20.0 mL (total) of NaOH is added
d. 50.0 mL (total) of NaOH is added
e. 100.00 mL (total) of NaOH is added
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Acids-Bases Equilibria
AP Chemistry
f. 150.0 mL (total) of NaOH is added
g. 200.0 mL (total) of NaOH is added
12) Consider the titration of 50.0 mL of 0.10 M acetic acid (Ka = 1.8 x 10-5) with 0.10 NaOH.
Calculate the pH of the solution at the following points:
a. Before NaOH is added
b. 10.0 mL of NaOH is added
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Acids-Bases Equilibria
AP Chemistry
c. 25.0 mL (total) of NaOH is added
d. 40.0 mL (total) of NaOH is added
e. 50.0 mL (total) of NaOH is added
f. 60.0 mL (total) of NaOH is added
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Acids-Bases Equilibria
AP Chemistry
g. 75.0 mL (total) of NaOH is added
13) Hydrogen cyanide gas, a powerful respiratory inhibitor, is highly toxic. It is a very weak
acid with a Ka = 6.2 x 10-10 when dissolved in water. If a 50.0 mL sample of 0.100 M
HCN is titrated with 0.100 M NaOH, calculate the pH of the solution.
a. After 8.00 mL of 0.100 M NaOH has been added
b. At the halfway point of titration
c. At the equivalence point of the titration
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Acids-Bases Equilibria
AP Chemistry
14) A chemist has synthesized a monoprotic weak acid and wants to determine tis Ka value.
To do so, the chemist dissolves 2.00 mmol of the solid acid in 100.0 mL water and
titrates the resulting solution with 0.0500 M NaOH. After 20.0 mL NaOH has been
added, the pH is 6.00. What is the Ka value for the acid?
15) You have 75.0 mL of 0.10 M HA. After adding 30.0 mL of 0.10 M NaOH, the pH is
5.50. Calculate the Ka value of HA.
16) A titration of 100.0 mL of a 0.050 M NH3 is conducted with a 0.10 M HCl solution.
Calculate the pH of the solution at the following points:
a. Before the addition of HCl
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Acids-Bases Equilibria
AP Chemistry
b. Before the equivalence point
c. At the equivalence point
d. Beyond the equivalence point
17) Bromothymol blue, an indicator with a Ka = of 1.0 x 10-7, is yellow in its HIn form and
blue in it’s In- form. Suppose one puts a few drops of the indicator in a strongly acidic
solution. If the solution is then titrated with NaOH, at what pH will the indicator color
change first be visible?
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