The pH of neutral water at 25°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°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°C is 7.0.
At 25°C, [H+]=[OH-]=10-7
and Kw=[H+][OH-]=10-14
On heating, Kw increases, i.e., [H+][OH-]>10-14
As [H+]=[OH]- or, [H+]2>=10-14
or, [H+]>10-7M
 pH<7
With rise in temperature, pH of pure water decreases and it become less than 7 at 60°C.