The graph shows the pH of a solution of a weak acid, HA, as a function of temperature - HSC - SSCE Chemistry - Question 9 - 2060 - Paper 1

As the temperature decreases, the pH of the solution increases. This is due to the fact that weak acids tend to dissociate more as temperature decreases, leading to a lower concentration of hydrogen ions ( ext{H}^+) in the solution. Therefore, the acidity of the solution decreases, resulting in a higher pH value.

For example, if we observe the graph, at lower temperatures (around 0°C), the pH tends to be higher (around 7.5), while at higher temperatures (around 200°C), the pH drops to approximately 5.5. This indicates that the solution becomes more acidic as the temperature increases.