Question

The sodium salt of a certain weak monobasic organic acid is hydrolysed to an extent of 3% in its 0.1 M solution at ${25}^{\circ }C$ given that the ionic product of water is ${10}^{-14}$ at this temperature, what is the dissociation constant of the acid?

• A. $1.1\times {10}^{-10}$
• B. $1.1\times {10}^{-9}$
• C. $3.33\times {10}^{-9}$
• D. $3.33\times {10}^{-10}$

Answer 1

The correct option is (A) $1.1\times {10}^{-10}$
The relationship between the hydrolysis constant $K_h$, the degree of hydrolysis h, and the salt concentration C is as given below.
$K_h=C\times h^2=0.1\times {\left(\frac{3}{100}\right)}^2=9\times {10}^{-5}$
The relationship between the acid dissociation constant $K_a$ , the ionic product of water $K_w$and the hydrolysis constant $K_h$

​$K_a$ = $\frac{K_w}{K_h}$ = $\frac{{10}^{-14}}{9\times {10}^{-5}}$ = 1$\times {10}^{-10}$