Question

The concentration at which degree of dissociation of a $0.02M$ solution of $C{H}_{3}COOH$ becomes double is: $(K_a$ of $C{H}_{3}COOH=1.8\times {10}^{-5})$

• A. $0.1M$
• B. $0.009M$
• C. $0.4M$
• D. $0.049M$

Answer 1

Answer: (D)

$0.049M$

Applying the Oswald dilution formula-

$K_a={\alpha }^2$

Now,

$K_a=C_{C}1\left({\alpha }^2\right)$ (i)

$K_a=C_2(2\alpha {)}^2$ (ii)

$C_2=\frac{C_1}{4}=\frac{0.02}{4}=0.05\approx 0.049M$