Question

A weak acid $HX$ has the dissociation constant $1\times {10}^{-5}M$. It forms a salt $NaX$ on reaction with alkali. The degree of hydrolysis of $0.1M$ solution of $NaX$ is:

• A. $0.0001$%
• B. $0.01$%
• C. $0.1$%
• D. $0.15$%

Answer 1

Answer: (B)

$0.01$%

$NaX+H_{2}O\to HX+NaOH$ or $X^{-}+H_{2}O\to HX+O{H}^{-}$

Let 'h' be degree of hydrolysis

$K_h=\frac{K_w}{K_a}=\frac{{C^{2}h}^2}{C(1-h)}\simeq C{h}^2$

$\frac{{10}^{-14}}{{10}^{-5}}=\frac{{C^{2}h}^2}{C(1-h)}\simeq 0.1h^2$

$h={10}^{-4}$ or $0.01$%