Question

The ka values of acetic acid and chloroacetic acid are 1.8 10-5 and 1.4 10-3, respectively. (a) Calculate the pH of a 0.40 M solution of acetic acid. (b) Calculate the pH of a 0.015 M solution of chloroacetic acid.

Answer 1

The pH of a 0.40 M solution of acetic acid is approximately 2.57. The pH of a 0.015 M solution of chloroacetic acid is approximately 4.68.

Step-by-step explanation:

(a) The initial pH is computed for the acetic acid solution in the usual ICE approach:
[H₃O⁺] = Ka × [CH₃CO₂H] = √1.8 × 10⁻⁵ × 0.400 = 2.68 × 10⁻³
pH = -log(2.68 × 10⁻³) = 2.57

(b) The initial pH is calculated for the chloroacetic acid solution in the same way:
[H₃O⁺] = Ka × [CClCO₂H] = 1.4 × 10⁻³ × 0.015 = 2.1 × 10⁻⁵
pH = -log(2.1 × 10⁻⁵) = 4.68