Question

The degree of dissociation of an acid $HA$ of $0.1M$ solution is $0.1$ %. Its dissociation constant is :

• A. $1\times {10}^{-3}$
• B. $1\times {10}^{-10}$
• C. $1\times {10}^{-7}$
• D. $1\times {10}^{-14}$

Answer 1

The correct option is C $1\times {10}^{-7}$

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, $K_a=C\times {\alpha }^2=0.1\times {\left(\frac{0.1}{100}\right)}^2=1\times {10}^{-7}.$

Option C is correct.