What is the value of pOH if a buffer solution is prepared by mixing equal volumes of $0.4 \mathrm{M}…
What is the value of pOH if a buffer solution is prepared by mixing equal volumes of $0.4 \mathrm{M} \mathrm{NH}_4 \mathrm{OH}$ and $0.5 \mathrm{M} \mathrm{NH}_4 \mathrm{Cl}$ solutions. $\left(\mathrm{pK}_{\mathrm{b}}=4.730\right)$
6.0
4.83
10.42
7.81
Solution
For a basic buffer,
$\begin{aligned}
\mathrm{pOH} & =\mathrm{pK}_{\mathrm{b}}+\log \frac{[\text { Salt }]}{[\text { Base }]} \\
& =4.730+\log \left(\frac{0.5}{0.4}\right) \\
& =4.83
\end{aligned}$