Question

A potassium hydroxide (KOH) solution has a molar concentration of 0.065 M, calculate the [H3O+], [OH-] and pH of the solution.

Answer 1

1) [OH⁻] = 0.065 M

2) [H₃O⁺] = 1.54 x 10⁻¹³ M.

3) pH = 12.81.

Explanation:

HCl is completely dissociated yo its ions in solution:

KOH + H₂O → H₃O⁺ + K⁺ + OH⁻,

1) [OH⁻] = 0.065 M.

2) [H₃O⁺]:

∵ [H₃O⁺][OH⁻] = 10⁻¹⁴.

∴ [H₃O⁺] = 10⁻¹⁴/[OH⁻] = 10⁻¹⁴/(0.065 M) = 1.54 x 10⁻¹³ M.

3) pH:

For strong acids like HCl:

pH = - log[H₃O⁺] = - log[1.54 x 10⁻¹³ M] = 12.81.