A laboratory stores an aqueous solution that initially has a measured pH of 9.25 at 25 °C
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A laboratory stores an aqueous solution that initially has a measured pH of 9.25 at 25 °C. The solution is then warmed to 60 °C for an experiment. Assume that the hydroxide-ion concentration remains constant during the temperature change. At 60 °C the autoionization constant of water is Kw=9.6×10−14.
(a) At 25 °C, calculate the pOH of the solution and determine [OH−].
(b) Using the given value of Kw at 60 °C, calculate pKw and then determine the new pH of the solution after it is warmed.
(c) Indicate whether the warmed solution is acidic, basic, or neutral relative to the neutrality point at 60 °C, and justify numerically.
(d) Provide a molecular-level explanation for why the pH changes even though no additional acid or base is introduced to the system.