Question

What is the $pOH$ of $0.1MKB$ (salt of weak acid and strong base) at $25^{\circ }C?$ (Given: $p{K}_b$ of $B^{-}=7)$

Answer 1

Answer: 4

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