Question

What is the $pOH$ of $0.1MKB$ (salt of weak acid and strong base) at $25^{\circ} C ?$ (Given: $pK _{ b }$ of $\left. B ^{-}=7\right)$

Answer 1

For salt of weak acid and strong base;
$\mathrm{pH}=7+\frac{1}{2} \mathrm{pK}_{\mathrm{a}}+\frac{1}{2} \log \mathrm{C}\left(\right.$ at $\left.25^{\circ}\right)$
$=7+\frac{1}{2}\times 7+\frac{1}{2}log10^{- 1}$
$=7+3.5-0.5$
$\therefore pH=10$
So, $\mathrm{pOH}=4$ (at $\left.25^{\circ} \mathrm{C}\right)$