Question

Accumulation of lactic acid $\left(H{C}_3{H}_5{O}_3\right),$ a monobasic acid in tissues leads to pain and a feeling of fatigue. In a 0.10 M aqueous solution, lactic acid is 3.7% dissociates. The value of dissociation constant, $K_a,$ for this acid will be

• A. $1.4\times {10}^{-5}$
• B. $1.4\times {10}^{-4}$
• C. $3.7\times {10}^{-4}$
• D. $2.8\times {10}^{-4}$

Answer 1

The correct option is B $1.4\times {10}^{-4}$

Degree of dissociation, $\alpha =\frac{3.7}{100}=0.037$ According to Ostwald's formula,
$K_a={\alpha }^{2}C=(0.037{)}^2\times 0.10=1.369\times {10}^{-4}\approx 1.4\times {10}^{-4}$