Question

why pH of solution changes with temperature

Answer 1

the pH changes due to change in temperature because at higher temperature an acid dissociates in H+ ions at a much faster rate.
Therefore temperature is directly proportional to pH level of an acid or base.

Hope this helps you ,,,,

Answer 2

if the pH falls as temperature increases, this does not mean that water becomes more acidic at higher temperatures. A solution is acidic if there is an excess of hydrogen ions over hydroxide ions (i.e., pH < pOH). ... At 100°C, the pH of pure water is 6.14, which is "neutral" on the pH scale at this higher temperature....