Question

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 ?
A. Equal to 7.0
B. Greater than 7.0
C. Less than 7.0
D. Equal to zero

Answer 1

Correct Answer - C
At `25^(@)C, [H^(+)]=[OH^(-)]=10^(-7) and K_(w) = [H^(+)][OH^(-)]=10^(-14)`. On heating, `K_(w)` increases , i.e, `[H^(+)][OH^(-)] gt 10^(-14)`. As `[H^(+)]=[OH^(-)],[H^(+)]^(2) gt 10^(-14) ` or `[H^(+)] gt 10^(-7) M or pH lt 7`.