Question

For 1 M solution of HA, the dissociation constant $K_a$ in terms of vant Hoff factor (i) can be written as :

• A. $\frac{(i-1{)}^2}{i}$
• B. $\frac{(i+1{)}^2}{i}$
• C. $\frac{i}{(i-1{)}^2}$
• D. $\frac{(i-1{)}^2}{(2-i)}$

Answer 1

Answer: (D)

$\frac{(i-1{)}^2}{(2-i)}$

$HA\rightleftharpoons H^{+}+A^{-}$
$i=1+\alpha$
$\Rightarrow \alpha =(i-1)$
Now, $K_a=\frac{C{\alpha }^2}{1-\alpha }\Rightarrow K_a=\frac{(i-1{)}^2}{1-(i-1)}$
$\Rightarrow K_a=\frac{(i-1{)}^2}{2-i}$