Question

A 0.20 M solution of methanoic acid has a degree of dissociation 0.032. Its dissociation constant is:

• A. 1.1 x 10${}^{-6}$
• B. 2.1 x 10${}^{-10}$
• C. 2.1 x 10${}^{-4}$
• D. 9.6 x 10${}^{-8}$

Answer 1

The correct option is C 2.1 x 10${}^{-4}$

According to ostwald dilution law, the dissociation constant $\left(K_a\right)$ is equal to the product of molar concentration $\left(C\right)$ and the square of the degree of dissociation $\left({\alpha }^2\right)$.

Hence, $K_a=C\times {\alpha }^2=0.20\times {\left(0.032\right)}^2=2.1\times {10}^{-4}.$

Hence, the correct option is $\text{C}$