Solution of 0.1 N NH₄OH and 0.1 N NH₄Cl has pH 9.25 . Then fine out pKb of NH₄OH

Options

(a) 9.25
(b) 4.75
(c) 3.75
(d) 8.25

Correct Answer:

4.75

Explanation:

Solution of 0.1 N NH₄OH and 0.1 N NH₄Cl is a buffer solution.
According to Henderson equation,
The pH of a basic buffer,
pH = 14 -pK(b) – log{C(salt)/C(base)}.
⇒pK(b) = 14-pH-log{C(salt)/C(base)},
⇒ pK(b) = 14-9.25-log{0.1/0.1}.
⇒ pK(b) = 14-9.25 = 4.75.
Therefore pK(b) of NH₄OH = 4.75.