Chemistry - Ionic Equilibrium Question with Solution | TestHub

${\text{pK}}_{\text{a}}\text{=}-\text{log}{\text{K}}_a\text{=}-\text{log}\text{(2}\times {\text{10}}^{-5})$
$=5-\mathrm{l}\mathrm{o}\mathrm{g}\mathrm{ }2=5-0.3=4.7$
$\text{pH}\text{=}\frac{\text{1}}{\text{2}}\left({\text{pK}}_{\text{w}}\text{+}{\text{pK}}_{\text{a}}\text{+}\text{log}\text{C}\right)$
$\mathrm{p}\mathrm{H}=\frac{1}{2}[14+4.7+\log \left(0.04\right)]$
$\mathrm{p}\mathrm{H}=8.63$
$\text{pOH}\text{=}\text{14}-\text{8}\text{.63}\cong \text{5}\text{.3}$
$\left[{\mathrm{O}\mathrm{H}}^{-}\right]=5\times {10}^{-6}$