Question

The sodium salt of a certain weak mono basic 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. $\approx 1\times {10}^{-10}$
• B. $\approx 1\times {10}^{-9}$
• C. $3.33\times {10}^{-9}$
• D. $3.33\times {10}^{-10}$

Answer 1

The correct option is A $\approx 1\times {10}^{-10}$

The relationship between the hydrolysis constant $K_h$, the degree of hydrolysis h and the salt concentration C is as given below.
$K_h=C\times h^2=0.1\times (\frac{3}{100}{)}^2=9\times {10}^{-5}$
The relationship between the acid dissociation constant $K_a$, the ionic product of water $K_w$ and the hydrolysis constant $K_h$
$K_a=\frac{K_w}{K_h}=\frac{{10}^{-14}}{9\times {10}^{-5}}\simeq 1\times {10}^{-10}$