Q19 / 180 · COMEDK 2023 (Memory Based) · Chemistry
In a $0.2 \mathrm{M}$ aqueous solution, lactic acid is $6.9 \%$ dissociated. The value of dissociation constant is
- A$1.2 \times 10^{-4}$
- Correct answerB$95 \times 10^{-4}$
- C$6.5 \times 10^{-4}$
- D$3.6 \times 10^{-2}$
Solution
Given, $\alpha=6.9 \%$
$\therefore$ Degree of dissociation, $\alpha=\frac{6.9}{100}$
$\therefore \quad \alpha=0.069$
According to ostwald's dilution law,
$\begin{aligned}
& K_a=\alpha^2 C=(0.069)^2 \times 0.2 \\
& K_a=9.5 \times 10^{-4}
\end{aligned}$
Hence, the correct answer is option: 'B'.