AP Chemistry
Worksheet : Ch. 14 ; obj 19-22
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1. For each of the following reactions, identify the acid, the base, the conjugate base, and the conjugate acid.
a. Fe(H2O)63+ + H2O ↔ Fe(H2O)5(OH)2+ + H3O+
b. C2H5NH+ + H2O ↔ H3O+ + C2H5N
2. At 0°C, the value of Kw is 1.14 x I0-15.
a. Calculate the [H+] and [OH-] in pure water at 0°C.
b. What is the pH of pure water at 0°C?
3. Calculate the concentration of an aqueous HNO3 solution that has pH = 4.25.
Not Review (Ka = 4.0 x 10-4)
4. What are the major species present in 0.250 M solutions of each of the following acids? Calculate the pH of
each of these solutions.
a. HNO2(Ka = 4.0 x 10-4)
b. CH3CO2H (HC2H3O2) (Ka = 1.8 x 10-5)
5. Calculate the concentrations of all species present and the pH of a 0.20 M HC2H3O2 solution.(Ka = 1.8 x 105
)
6. Boric acid (H3BO3) is commonly used in eyewash solutions in chemistry laboratories to neutralize bases
splashed in the eye. It acts as a monoprotic acid, but the dissociation reaction is slightly different from that
of other acids:
B(OH)3 + H2O ↔B(OH)4- + H+
Ka = 5.8 x 10-10
Calculate the pH of a 0.50 M solution of boric acid.
7. A solution is prepared by dissolving 12.2 g benzoic acid (C6H5CO2H, Ka = 6.4 x 10-5) in enough water to
make 1.00 L of solution. Calculate [C6H5CO2H], [C6H5CO2-], [H+], [OH-], and the pH in this solution.
8. Calculate the concentration of all species present and the pH of a 0.020 M HF solution. (Ka = 7.2 x 10-4)
9. Formic acid (HCO2H) is secreted by ants. Calculate [H+] and the pH of a 0.025 M solution of formic acid
(Ka = 1.8 x 10-4).
10. Monochloroacetic acid, HC2H2C1O2, is a skin irritant that is used in "chemical peels" intended to remove
the top layer of dead skin from the face and ultimately improve the complexion. The value of Ka for
monochloroacetic acid is 1.35 x 10-3. Calculate the pH of a 0.10 M solution of monochloroacetic acid.
11. Calculate the pH of a solution containing a mixture of 0.10 M HCl and 0.10 M HOCl. (KaHOCL = 3.5 x 10-8)
12. Calculate the pH of solution that contains 1.0 M HF(Ka = 7.2 x 10-4) and 1.0 M HOC6H5(Ka = 1.6 x 10-10).
Also calculate the concentration of OC6H5- in this solution at equilibrium.
13. Calculate the percent dissociation of the acid in each of the following solutions.
a. 0.50 M acetic acid(Ka = 1.8 x 10-5)
b. 0.050 M acetic acid(Ka = 1.8 x 10-5)
c. 0.0050 M acetic acid(Ka = 1.8 x 10-5)
d. Use Le Chatelier's principle to explain why percent dissociation increases as the concentration of a
weak acid decreases.
e. Even though the percent dissociation increases from solutions a to c, the [H+] decreases. Explain.
14. For propanoic acid (HC3H5O2, Ka = 1.3 x 10-5), calculate the [H+], pH, and percent dissociation of a 0.10
M solution.
15. A 0.15 M solution of a weak acid is 3.0% dissociated. Calculate Ka.
16. The pH of a 0.063 M solution of hypobromous acid (HOBr but usually written HBrO) is 4.95. Calculate
Ka.
17. A typical sample of vinegar has a pH of 3.0. Assuming that vinegar is only an aqueous solution of acetic
acid (Ka = 1.8 x 10-5), calculate the concentration of acetic acid in vinegar.
Answers : 1a. Acid: Fe(H2O) 63+, base : H2O, CB : Fe(H2O)5(OH)2+ CA: H3O+ 1b. Acid: C2H5NH+, base :
H2O, CB : C2H5N CA: H3O+ 2a. [H+] = 3.38 x 10-8 M 2b. 0ºC pH = 7.471 3. 5.6 x 10-5 M HNO3 4a.
Major species = HNO2 and H2O , pH = 2.00 (solve as equilibrium problem) 4b. CH3CO2H and water are the
major species, pH = 2.68 5. Major species : HC2H3O2 and water, [H+] = [C2H3O2-] = 1.9 x 10-3 M, [OH-] =
5.3 x 10-12M, [HC2H3O2] = 0.20 M, pH = 2.72 6. pH = 4.77 7. [C6H5CO2-] = [H+]= 2.5 x 10-3 M,
[C6H5CO2H] = 9.74 x 10-2 M, [OH-] = 4.0 x 10-12 M, pH = 2.60 8. [H+] = [F-] = 3.5 x 10-3 M, [OH-] = 2.9 x
10-12 M, [HF] = 0.017 M, pH = 2.46 9. [H+] = 2.0 x 10-3, pH = 2.70 10. pH = 1.96
11. pH = 1.00 12.
pH = 1.57, [OC6H5-] = 5.9 x 10-9 M 13a. 0.60% 13b. 1.9% 13c. 5.8% 13d. Q>Ka so shift is to the right
13e. [H+] depends on initial concentrations of the weak acids and how much the weak acid dissociates. For
solutions a-c the initial concentration of acid decreases more rapidly than the percent dissociation increases.
Thus, [H+] decreases. 14. [H+] = 0.0011, pH = 2.96, 1.1% 15. Ka = 1.4 x 10-4
16. Ka = 1.9 x 10-9
-2
17. 6 x 10 M