Q. The pH of a 0.1 M solution of $NH_{4}OH$ (having $K_{b} = 1.0 \times 10^{- 5})$ is equal to

A) 10
B) 6
C) 11
D) 12
Explanation

(c)
$\left\lbrack {OH}^{-} \right\rbrack = \sqrt{K_{b} \times C}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ = \sqrt{1 \times 10^{- 5} \times 10^{- 1}}$
$= \sqrt{10^{- 6}} = 10^{- 3}$
$K_{w} = \left\lbrack H^{+} \right\rbrack\lbrack{OH}^{-}\rbrack$
$10^{- 14} = \left\lbrack H^{+} \right\rbrack\lbrack 10^{- 3}\rbrack$
$\left\lbrack H^{+} \right\rbrack = 10^{- 11}$
Hence, $pH = - \log H^{+}$
$= - \log{(1 \times 10^{- 11})} = 11$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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