Question

Solution of $0.1 \,N\, NH_4OH$ and 0.1 N $NH_4Cl$ has pH 9.25. Then $pK_b$ of $NH_4OH$ :-

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

Answer 1

Answer: (B)

4.75

Answer 2

The correct option is(B): 4.75.

Solution of $NH_4OH$ and $NH_4Cl$ acts as a basic buffer solution. For basic buffer solution
$pOH = PK_b + \log \frac{[salt]}{[base]}$
$pOH = 14 - pH$
$= 14 - 9.25 = 4.75$
$4.75 = pK_b + log \frac{0.1}{0.1}$
$pK_b = 4.75$