CH160 Acid-Base Chemistry Ch. 17, Section 1-4 Example Problems This list of acid-base chemistry problems contains problems that will be worked as examples in class and additional problems for students to try on their own. 1. (a) Calculate the % ionization of the acid and the pH of the solution that contains 0.500 M acetic acid, CH3COOH (Ka = 1.8 x 10-5), and 0.200 M sodium acetate, CH3COONa. Ans. pH = 4.34, 0.0090% (b) Calculate the % ionization of the acid and the pH of the solution that contains 0.040 M acetic acid, CH3COOH (Ka = 1.8 x 10-5), and 0.080 M sodium acetate, CH3COONa. Ans. pH = 5.05, 0.023% (c) Calculate the % ionization of the base and the pH of the solution that contains 0.10 M dimethylamine, (CH3)2NH (Kb = 5.4 x 10-4), and 0.12 M dimethylammonium chloride, (CH3)2NH2+. Ans. pH = 10.64, 0.45% 2. (a) Calculate the pH of a buffer solution that contains 0.25 M sodium acetate, CHCOONa, and 0.35 M acetic acid, CH3COOH (Ka = 1.8 x 10-5). 3 Ans. 4.60 (b) Calculate the pH of a buffer solution that contains 0.40 M dimethylamine, (CH3)2NH (Kb = 5.4 x 10-4), and 0.50 M dimethylammonium chloride, (CH3)2NH2+ (K = 1.9 x 10-11). a Ans. 10.62 (c) Calculate the pH of a buffer that is prepared by mixing 500.0 mL of 0.25 M acetic acid, CH3COOH (Ka = 1.8 x 10-5), with 500.0 mL of 0.17 M sodium acetate, CH3COONa. Ans. 4.58 12 3. (a) Calculate the pH of the solution formed by adding 0.050 moles HCl to 500.0 mL of the buffer in Example 2a. What is the change in pH that occurs in the buffer solution? Calculate the change in pH that occurs when 0.050 moles HCl are added to 500.0 mL of pure water? Ans. pH = 4.27, ∆pH = -0.33, ∆pH = -6 (b) Calculate the pH of the solution formed by adding 0.025 moles NaOH to 500.0 mL of the buffer in Example 2a. What is the change in pH that occurs in the buffer solution? Ans. pH = 4.74, ∆pH = +0.14 (c) Calculate the pH of the solution formed by adding 0.50 g of NaOH to 500.0 mL of the buffer in Example 2a. What is the change in pH that occurs in the buffer solution? Ans. pH = 4.67, ∆pH = +0.07 (d) Calculate the pH of the solution formed by mixing 1.0 mL of 6.0 M HCl(aq) with 500.0 mL of the buffer in Example 2a. What is the change in pH that occurs in the buffer solution? Ans. pH = 4.56, ∆pH = -0.04 4. Starting with 1.0 L of 0.100 M CH3COOH, how would you prepare a CH3COOH (K = 1.8 x 10a Ans. Add 3.7 g CH-5)/CH3COONa (FW = 82 g/mol) buffer with a pH of 4.40? 3COONa to 1.0 L of 0.100 M CH3COOH 5. Calculate the pH for the solution formed after mixing 25.0 mL of 0.100 M HCl(aq) with (a) 10.0 mL, (b) 25.0 mL and (c) 35.0 mL of 0.100 M NaOH(aq). Ans. (a) pH = 1.37, (b) pH = 7.0, (c) pH = 12.22 6. Calculate the concentration of an HCl solution if 25.0 mL of this solution requires 18.0 mL of 0.150 M NaOH(aq) to reach the equivalence point. Ans. 0.108 M 7. Calculate the pH for the solution formed after mixing 25.0 mL of 0.100 M acetic acid, CH3COOH (Ka = 1.8 x 10-5), with (a) 10.0 mL, (b) 25.0 mL, and (c) 35.0 mL of 0.100 M NaOH(aq). Ans. (a) pH = 4.57, (b) pH = 8.72, (c) pH = 12.22 8. Calculate the pH for the solution formed after mixing 25.0 mL of 0.100 M NH3 (Kb = 1.8 x 10-5), with (a) 10.0 mL, (b) 25.0 mL, and (c) 35.0 mL of 0.100 M HCl(aq). Ans. (a) pH = 9.43, (b) pH = 5.28, (c) pH =