Question

Pure water has pH = 7 (neutral) at ${25}^{\circ }C$. What will be the nature of the pH of water at ${75}^{\circ }C$ ?

• A. Acidic
• B. Basic
• C. Neutral
• D. Unpredictable

Answer 1

The correct option is C Neutral

$H_{2}O\leftrightharpoons H^{+}+O{H}^{-}$
This is an endothermic reaction.
As the temperature increases, more $H_{2}O$ molecules dissociate. The ionic product of water $\left(K_w\right)$ increases and as a result ,the $pH$ will decrease but water will still remain neutral. It will not become acidic because there will always be the same concentration of $H^{+}$ and $O{H}^{-}$ ions. The neutral point will shift to a value lower than 7 in $pH$ scale.