The autoionization constant of water increases with temperature
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
The autoionization constant of water increases with temperature. At 25 °C the value of Kw is 1.0×10−14, while at 40 °C it is 2.92×10−14. A chemistry student notices that a perfectly pure sample of water at 40 °C does not register a pH of 7.00 on a high-precision meter and wants to understand why.
(a) Calculate pKw at 40 °C to two decimal places.
(b) Determine the pH of neutral water at 40 °C.
(c) Explain, in terms of the temperature dependence of the autoionization equilibrium, why the pH of neutral water at 40 °C differs from 7.00 even though the solution contains no added acid or base.