Which of the following statement(s) is/are correct? (A) The pH of 1 × 10 – 8   M   HCl…

When concentration of ${\mathrm{H}}^{+}$ ion is more than ${10}^{-7}\mathrm{M}$, the proton concentration from water must be considered. Hence, the pH of ${10}^{-8}\mathrm{M} \mathrm{HCl}$ solution is not equal to 8.

$\underset{\mathrm{Acid}}{{\mathrm{H}}_2{\mathrm{PO}}_4^{-}}\stackrel{}{\rightleftharpoons }\underset{\mathrm{Conjugate} \mathrm{base}}{{\mathrm{HPO}}_4^{2-}}+{\mathrm{H}}^{+}$

${\mathrm{K}}_{\mathrm{w}}$ increase with increase in temperature as dissociation of water increases with increase in temperature.

When weak monoprotic acid is titrated against strong base, at half neutralization point, the solution becomes acidic buffer and its $\mathrm{pH}$ is given by

$\mathrm{pH}={\mathrm{pK}}_{\mathrm{a}}+\log \frac{\left[\mathrm{Salt}\right]}{\left[\mathrm{Acid}\right]}$

$\Rightarrow \mathrm{pH}={\mathrm{pK}}_{\mathrm{a}}+0$ as $\left[\mathrm{salt}\right]=\left[\mathrm{acid}\right]$