Q62 / 180 · NEET 2013 (Karnataka) · Chemistry
Accumulation of lactic acid $\left(\mathrm{HC}_3 \mathrm{H}_5 \mathrm{O}_3\right)$, a monobasic acid in tissues leads to pain and a feeling of fatigue. In a 0.10
$\mathrm{M}$ aqueous solution, lactic acid is $3.7 \%$ dissociates. The value of dissociation constant, $\mathrm{K}_a$, for this acid will be:
- A$1.4 \times 10^{-5}$
- Correct answerB$1.4 \times 10^{-4}$
- C$3.7 \times 10^{-4}$
- D$2.8 \times 10^{-4}$
Solution
$$
\alpha=\frac{3.7}{100}=0.037
$$
According to Ostwald's formula
$$
\begin{aligned}
\mathrm{K}_\alpha & =\alpha^2 \mathrm{C} \\
& =(0.037)^2 \times 0.10 \\
& =1.369 \times 10^{-4}
\end{aligned}
$$
Hence, the correct answer is option: 'B'.