Question

The dissociation constant of a weak acid HA is $4.9\times {10}^{-7}$. Percentage ionisation :

• A. $0.03$%
• B. $0.07$%
• C. $0.27$%
• D. $0.1$%

Answer 1

The correct option is B $0.07$%

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

We can use the formula, $\alpha =\sqrt{\frac{K{a}^2}{C}}$

$\alpha$ =$\sqrt{\frac{(4.9\times {10}^{-7})}{1}}$

So $\alpha$ = $7\times {10}^{-4}$

therefore, percentage ionisation = $\frac{(7\times {10}^{-4})}{1}\times 100$ = $0.07$%