Question

Solution of $0.1\, N\, NH _{4} OH$ and $0.1\, N\, NH _{4} Cl$ has $pH 9.25$, then find out $pK _{ b }$ of $NH _{4} OH$.

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

Answer 1

Answer: (B)

4.75

Answer 2

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