The pH of neutral water at 25°C is 7 .O. 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°C?

The pH of neutral water at 25°C is 7.0.

$$\begin{gathered} \text{ At }{25}^{\circ }\mathrm{C},\left[{\mathrm{H}}^{+}\right]=\left[{\mathrm{OH}}^{-}\right]={10}^{-7} \\ \mathrm{and} {\mathrm{K}}_{\mathrm{W}}=[\mathrm{H}{]}^{+}\left[{\mathrm{OH}}^{-}\right]={10}^{-14} \\ \text{ On heating, }{\mathrm{K}}_{\mathrm{w}}\text{ increases, i.e. }\left[{\mathrm{H}}^{+}\right]\left[{\mathrm{OH}}^{-}\right]>{10}^{-14} \\ \text{ As }\left[{\mathrm{H}}^{+}\right]=\left[{\mathrm{OH}}^{-}\right]\text{or, }{\left[{\mathrm{H}}^{+}\right]}^2>={10}^{-14} \\ \mathrm{or} \left[{\mathrm{H}}^{+}\right]>{10}^{-7}\mathrm{M} \\ \mathrm{pH}<7 \\ \mathrm{With} \mathrm{rise} \mathrm{in} \mathrm{temperature}, \mathrm{pH} \mathrm{of} \mathrm{pure} \mathrm{water} \mathrm{decreases} \mathrm{and} \mathrm{it} \mathrm{become} \mathrm{less} \mathrm{than} 7 \mathrm{at} 60°\mathrm{C}. \end{gathered}$$