The K w for water at 0 ∘ C is 0.12 * 10 - 14 M 2. Calculate the pH of a neutral aqueous solution at 0 ∘ C. p H = Is a pH = 7.25 solution acidic, basic, or neutral at 0 ∘ C?

pH → 7.46

Explanation:

We begin with the autoionization of water. This equilibrium reaction is:

2H₂O ⇄ H₃O⁺ + OH⁻ Kw = 1*10⁻¹⁴ at 25°C

Kw = [H₃O⁺]. [OH⁻]

We do not consider [H₂O] in the expression for the constant.

[H₃O⁺] = [OH⁻] = √1*10⁻¹⁴ → 1*10⁻⁷ M

Kw depends on the temperature

0.12*10⁻¹⁴ = [H₃O⁺]. [OH⁻] → [H₃O⁺] = [OH⁻] at 0°C

√0.12*10⁻¹⁴ = [H₃O⁺] → 3.46*10⁻⁸ M

- log [H₃O⁺] = pH

pH = - log 3.46*10⁻⁸ → 7.46