Question

A weak acid $HX(K_a=1\times {10}^{-5})$ on reaction with NaOH gives NaX. For 0.1 M aqueous solution of NaX, the % hydrolysis is:

• A. 0.001%
• B. 0.01%
• C. 0.15%
• D. 1%

Answer 1

Answer: (B)

0.01%

For NaX
$\underset{1-h}{X^{-}}+H_{2}O\rightleftharpoons \underset{h}{HX}+{\underset{h}{OH}}^{-}$

The expression for degree of hydrolysis can be given as:
$\therefore h=\sqrt{\frac{K_H}{C}}=\sqrt{\frac{K_w}{K_a\cdot C}}=\sqrt{\frac{{10}^{-14}}{{10}^{-5}\times 0.1}}$
$=\sqrt{{10}^{-8}}={10}^{-4}$
$\therefore$ % $h={10}^{-4}\times 100={10}^{-2}=0.01$