The pH of neutral water at $25°\mathrm{C}$ is 7.0. As the temperature increases, ionisation of water increases, however, the concentration of H+ ions and OH- ions are equal. What will be the pH of pure water at $60°\mathrm{C}$?

(1) Equal to 7.0

(2) Greater than 7.0

(3) Less than 7.0

(4) Equal to zero

(3) HINT:  With increase in temperature Kw increases.

The pH of neutral water at $25°\mathrm{C}$ is 7.0.
At
and ${\mathrm{K}}_{\mathrm{w}}=\left[{\mathrm{H}}^{+}\right]\left[{\mathrm{OH}}^{-}\right]={10}^{-14}$
On heating, Kw increases, i.e., $\left[{\mathrm{H}}^{+}\right]\left[{\mathrm{OH}}^{-}\right]>{10}^{-14}$
As
or, $\left[{\mathrm{H}}^{+}\right]>{10}^{-7}\mathrm{M}$
With rise in temperature, pH of pure water decreases and it become less than 7 at $60°\mathrm{C}$.