Question

A $0.010\, M$ solution of maleic acid, a monoprotic organic acid, is $14 \%$ ionised. What is $K_{a}$ for maleic acid?

• A. $2.3 \times 10^{-3}$
• B. $2.3 \times 10^{-4}$
• C. $2.0 \times 10^{-4}$
• D. $2.0 \times 10^{-6}$

Answer 1

Answer: (B)

$K_{a}=C \alpha^{2} /(1 / \alpha)$
where, $C=$ concentration $=0.01 M$
$\alpha=$ degree of dissociation $=14 \%=0.14$
$K_{a}=0.01 \times(0.14)^{2} /(1-0.14)$
$=\frac{1.96 \times 10^{-4}}{0.86}$
$=2.27 \times 10^{-4} \approx 2.3 \times 10^{-4}$