Question

A solution of $2M$ formic acid $\left(HCOOH\right)$ is $0.95$% ionized. What is the $K_a$ of formic acid?

• A. $1.9\times {10}^{-2}$
• B. $1.8\times {10}^{-4}$
• C. $9\times {10}^{-5}$
• D. $4.5\times {10}^{-5}$

Answer 1

The correct option is B $1.8\times {10}^{-4}$

We know that dissociation constant, $K_a={\alpha }^{2}C$

Where $\alpha$ is degree hydrolysis and $C$ is concentration.

$K_a={\left(\frac{0.95}{100}\right)}^2\times 2=1.8\times {10}^{-4}$