Question

How much must be a 0.02 M solution of sodium be diluted at 25⁰C in order to double the degree of hydrolysis?

• A. 0.25 time
• B. 2 times
• C. 4 times
• D. 8 times

Answer 1

The correct option is C

4 times

Let $h$ be the initial degree of hydrolysis.
$K_k={Ch}^2=0.2\times h+2\cdots \left(i\right)$
Let the concentration becomes $C_2$ when degree of hydrolysis is $2h$
$K_k=C_1(2h{)}^2=4C_i{h}^2\cdots (ii)$

Dividing Eqs. $\left(i\right)$ by $\left(ii\right)$,

$\frac{K_h}{K_k}=\frac{0.2h^2}{4C_1{h}^2},1=\frac{0.2}{4C_1},C_1=\frac{0.2}{4}=0.05M$

Now, from, $M_1{V}_1=M_2{V}_2,0.2V_1=0.05V_2$
$V_2=\frac{0.2}{0.05}{V}_1=4V_1$
Therefore, the solution must be diluted four times.