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 $1.1\times {10}^{-10}$

We know that $K_a$ for weak acid
$K_a=\frac{K_w}{K_h}{K}_h\to \text{Hydrolysis constant}{K}_h=C{\alpha }^2(C\to \text{concentration of salt})\Rightarrow K_h=0.1\times {\left(\frac{3}{100}\right)}^2(h\Rightarrow \text{degree of hydrolysis})\Rightarrow K_h=9\times {10}^{-5}\Rightarrow K_w={10}^{-14}\Rightarrow K_a=\frac{{10}^{-14}}{9\times {10}^{-5}}=1.1\times {10}^{-10}$