Question

The degree of dissociation of weak electrolyte is inversely proportional to the square root of concentration. It is called Ostwald's dilution law.

$\alpha =\sqrt{\frac{K_a}{c}}$, as the temperature increases, degree of dissociation will increase

$\frac{{\alpha }_1}{{\alpha }_2}=\sqrt{\frac{K_{a_1}}{K_{a_2}}}$, if concentration is same

$\frac{{\alpha }_1}{{\alpha }_2}=\sqrt{\frac{c_2}{c_1}}$, if acid is same

$a_1$ and $a_2$ are in ratio of $1:2,K_{a_1}=2\times {10}^{-4}$. What will be $K_{a_2}$?

• A. $8\times {10}^{-4}$
• B. $2\times {10}^{-4}$
• C. $4\times {10}^{-4}$
• D. $1\times {10}^{-4}$

Answer 1

The correct option is A $8\times {10}^{-4}$

For weak acids,

$\frac{{\alpha }_1}{{\alpha }_2}=\sqrt{\frac{K_{a_1}}{K_{a_2}}}$

Substituting,

$\frac{1}{2}=\sqrt{\frac{2\times {10}^{-4}}{K_2}}$

$K_2=8\times {10}^{-4}$