Question

The $p{K}_b$ value of $N{H}_3$ is 5. Calculate the $pH$ of the buffer solution, $1L$ of which contains $0.01MN{H}_{4}Cl$ and $0.10MN{H}_{4}OH$ :

• A. 4
• B. 6
• C. 8
• D. 10

Answer 1

Answer: (D)

$pOH=p{K}_b+\log \frac{[\text{ salt }]}{[\text{ base }]}$
Given : $p{K}_b=5$, [base $]=0.10M$,
[salt] $=0.01M$
$\therefore pOH=5+\log \frac{0.01}{0.10}=4$
$pH+pOH=14$
$\therefore pH=14-4=10$