Question

The $P^H$ of a weak mono basic acid is $5$. The degree of ionisation of acid in $0.1M$ solution is?

• A. ${10}^{-4}$
• B. ${10}^{-3}$
• C. ${10}^{-2}$
• D. ${10}^{-1}$

Answer 1

The correct option is A ${10}^{-4}$

Suppose $HA$ is a weak monobasic acid, on dissociation, it will give

$HA\to H^{+}+A^{-}$

$0.1$ 0 0 at initial state

$0.1(1-\alpha )$ $0.1\alpha$ $0.1\alpha$ after some time

Given that,

$P^H=5thus,{[H}^{+1}]={10}^{-5}=0.1\alpha$

$\therefore \alpha =\frac{{10}^{-5}}{0.1}={10}^{-4}$

Hence, option $A$ is correct.