Question

Solution of $0.1N$ $N{H}_{4}OH$ and $0.1N$ $N{H}_{4}Cl$ has $pH$ $9.25$, then find out $p{K}_b$ of $N{H}_{4}OH$ is:

• A. $9.25$
• B. $4.75$
• C. $3.75$
• D. $8.25$

Answer 1

Answer: (B)

$4.75$

Solution of $N{H}_{4}OH$ and $N{H}_{4}Cl$ acts as a basic buffer solution. For basic buffer solution,
$pOH=p{K}_b+\log \frac{\left[Salt\right]}{\left[Base\right]}$
$pOH=14-pH$
$=14-9.25=4.75$
$4.75=p{K}_b+\log \frac{0.1}{0.1}$
$p{K}_b=4.75$