Question

Degree of hydrolysis for a salt of strong acid and weak base is:

• A. independent of dilution
• B. increases with dilution
• C. increases with decrease in $K_b$ of the bases
• D. decreases with decrease in temperature.

Answer 1

Answer: (C)

increases with decrease in $K_b$ of the bases
Degree of hydrolysis, $h=\frac{\text{Amount of salt hydrolyzed}}{\text{Total salt taken}}$
$K_h=\frac{h^{2}C}{1-h}$
As $h$ is very small and $(1-h)$ $\to$ $1$,
$\Rightarrow h^2=K_h\times \frac{1}{C}$
$h=\sqrt{\frac{K_h}{C}}$
For salt of strong acid and weak base,
$K_h=\frac{K_w}{K_b}$
$\Rightarrow h=\sqrt{\frac{K_w}{K_{b}C}}$
Hence, is inversley proportional to $K_b$.