Chemistry - Ionic Equilibrium Question with Solution | TestHub

It is a salt of weak acid and strong base so acidic buffer is formed here, hence
$\mathrm{p}\mathrm{H}=\mathrm{p}{\mathrm{K}}_{\mathrm{a}}+\mathrm{l}\mathrm{o}{\mathrm{g}}_{10}\frac{\left[\mathrm{S}\mathrm{a}\mathrm{l}\mathrm{t}\right]}{\left[\mathrm{A}\mathrm{c}\mathrm{i}\mathrm{d}\right]}$
$\mathrm{p}\mathrm{H}=-\mathrm{l}\mathrm{o}\mathrm{g}5\times 10^{-10}+\mathrm{l}\mathrm{o}\mathrm{g}\left[\frac{\frac{5\times \mathrm{V}}{\mathrm{V}+10}}{\frac{10\times 2}{\mathrm{V}+10}}\right]$
or$9=-\mathrm{l}\mathrm{o}\mathrm{g}5\times 10^{-10}+\mathrm{l}\mathrm{o}\mathrm{g}\frac{\mathrm{V}}{4}$
So V = 2 mL