Question

Which of the following is true in pure water at any temperature?

A. [H₃O⁺] = [OH⁻]
B. Kw decreases with increasing temperature.
C. [H₃O⁺][OH⁻] = 1.0 x 10^-14
D. pH = 7.0

Answer 1

In pure water at any temperature, [H₃O⁺] = [OH⁻] is true, indicating equal concentrations of hydronium and hydroxide ions. The product of their concentrations, Kw, changes with temperature, only equating to 1.0 x 10^-14 at 25°C. The pH of pure water can deviate from 7.0 at temperatures other than 25°C.

Step-by-step explanation:

The question pertains to the properties of pure water at different temperatures. Considering the options provided:

• A. [H₃O⁺] = [OH⁻] is true in pure water at any temperature, because the number of hydronium ions will always equal the number of hydroxide ions in pure water.
• C. [H₃O⁺][OH⁻] = 1.0 x 10^-14 is only true at 25°C, but the product of these ion concentrations, known as the ionization constant for water (Kw), varies with temperature.

The other statements are false because:

• B. Kw increases with increasing temperature because the process of ionization of water is endothermic.
• D. pH = 7.0 is only true at 25°C; the pH of pure water can be lower at higher temperatures due to increased ionization.