Question

11. The Ka for benzoic acid is 6.5 × 10–5. Calculate the pH of a 0.10 M benzoic acid solution.

Answer 1

Answer:

2.6

Explanation:

Benzoic acid is a weak acid that dissociates according to the following equation.

C₆H₅COOH(aq) ⇄ C₆H₅COO⁻(aq) + H⁺(aq)

We can calculate the equilibrium concentration of H⁺ using the following expression.

[H⁺] = √(Ka × Ca)

where,

Ka is the acid dissociation constant

Ca is the initial concentration of the acid

[H⁺] = √(6.5 × 10⁻⁵ × 0.10) = 2.5 × 10⁻³

The pH is

pH = -log [H⁺] = - log 2.5 × 10⁻³ = 2.6