Question

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

• A. $0.001\%$
• B. $0.01\%$
• C. $0.10\%$
• D. $0.15\%$

Answer 1

Answer: (B)

$0.01\%$

It is given that a weak acid $HX$ has a dissociation constant value of $1\times {10}^{-5}M$.

It forms a salt $NaX$ on reaction with $NaOH$.

For a salt of a weak acid and a strong base, the expression for the degree of hydrolysis $h$ is given below:

$h=\sqrt{\frac{K_w}{K_a\times c}}=\sqrt{\frac{1\times {10}^{-14}}{1\times {10}^{-5}\times 0.1}}=0.0001$

Here, $K_w$ is the ionic product of water, $K_a$ is the dissociation constant and $c$ is the concentration.

Hence, the percentage degree of hydrolysis $=100\times 0.0001=0.01\%$