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).

• A. at 5 °C, K_w = 1.05×10⁻¹⁴
  at 45 °C, K_w = 3.00×10⁻¹⁴
• B. at 5 °C, K_w = 1.50×10⁻¹⁴
  at 45 °C, K_w = 3.50×10⁻¹⁴
• C. at 5 °C, K_w = 1.87×10⁻¹⁴
  at 45 °C, K_w = 3.88×10⁻¹⁴
• D. at 5 °C, K_w = 1.87×10⁻¹⁵
  at 45 °C, K_w = 3.88×10⁻¹⁴

Answer: (D)