Auto-Ionization Practice Problems

Temperature affects the dissociation of water into hydronium and hydroxide ions. At 5 °C, [H₃O⁺] = 4.32×10⁻⁸ mol/kg of water, at 25 °C, [H₃O⁺] = 1.00×10⁻⁷ mol/kg of water, and at 45 °C, [H₃O⁺] = 1.97×10⁻⁷ mol/kg of water. Determine if the dissociation of water into hydronium and hydroxide ions is endothermic or exothermic.

True or false: K_w is the product of [H₃O⁺] and [OH⁻] for water and is numerically equal to 1.0×10⁻⁷ at 25 °C.

Temperature affects the dissociation of water into hydronium and hydroxide ions. Given the molalities of hydronium ions at 5 °C, 25 °C, and 45 °C, calculate the values of K_w (in 3 s.f.) at 5 °C and at 45 °C (at 5 °C,  [H₃O⁺] = 4.32×10⁻⁸ mol/kg of water, at 25 °C, [H₃O⁺] = 1.00×10⁻⁷ mol/kg of water, and at 45 °C, [H₃O⁺] = 1.97×10⁻⁷ mol/kg of water).

What is the pH of pure water at 100°C where K_w is 51.3 x 10^-14?

Determine the K_w of pure water at 40°C. Its pH is 6.77.

At 50.0°C, K_w is 5.5 x 10^-14. Determine [OH^-] in pure water at this temperature.