Name _________________________________________________ Date ____________________ Period __
Homework
Chapter 16: Acid-Base Equilibria
Exercises: Sections 16.6, 16.7: Weak Acids; Weak Bases
1. Define an acid dissociation constant, Ka :
2. Write the chemical equation and the Ka expression for the acid dissociation of each of the following acids in
aqueous solution. Do not worry about phases of matter.
(a) HC6H5O;
(b) HCO3¯
3. Phenylacetic acid, HC8H7O2, is one of the substances that accumulates in the blood of persons with
disorder that can cause mental retardation or even death. A 0.085 M solution of this substance is found to
have a pH of 2.68. Calculate the Ka value for this acid.
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4. A 0.100 M solution of bromoacetic acid, BrCH2COOH, is 13.2 % ionized. Using this information, calculate
[BrCH2COO – ], [H+], [BrCH2COOH], and Ka for bromoacetic acid.
5. How many moles of HF (Ka = 6.8 x 10-4) must be present in 0.200 L to form a solution with a pH of 3.25?
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6. The acid-dissociation constant for hypochlorous acid, HClO, is 3.0 x 10 – 8. Calculate the concentrations of
H3O+, ClO –, and HClO at equilibrium if the initial concentration of the acid is 0.075 M. Calculate both
ways: 1) using the quadratic equation, and 2) ignoring the dissociation of the weak acid. Compare the
answers.
7. Determine the pH of each of the following solutions (Ka and Kb values are given in Appendix D in the
textbook):
(a) 0.125 M hypochlorous acid;
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7. Continued:
(b) 0.0085 M phenol;
(c) 0.095 M hydroxylamine
8. The active ingredient in aspirin is acetylsalicylic acid, HC9H7O4, a monoprotic acid with Ka = 3.3 x 10 – 4 at
25oC. What is the pH of a solution obtained by dissolving one aspirin tablet, containing 325 mg of
acetylsalicylic acid, in 250 mL of water?
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9. Calculate the percent ionization of HCrO4 – in solutions of each of the following concentrations (Ka is given
in Appendix D in the textbook):
(a) 0.250 M
(b) 0.0800 M
(c) 0.0200 M
10. What are two kinds of molecules or ions that commonly function as weak bases?
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11. Write the chemical equation and the Kb expression for the reaction of each of the following bases with
water:
(a) propylamine, C3H7NH2;
(b) monohydrogenphosphate ion, HPO42¯;
(c) benzoate ion, C6H5CO2¯.
12. Calculate the molar concentration of OH¯ ions in an 0.85 M solution of hypobromite ion, BrO –
(Kb = 4.0 x 10 – 6 ). What is the pH of this solution?
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13. Codeine, C18H21NO3, is a weak organic base. A 5.0 x 10 – 3 M solution of codeine has a pH of 9.95.
Calculate the value of Kb for this substance. What is pKb for this base?
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