Question

The dissociation constants of m-nitrobenzoic acid and acetic acid are $36.0\times {10}^{-5}$ and $1.8\times {10}^{-5}$ respectively. What are their relative strengths?

Answer 1

Relative strength is measured by degree of dissociation.

Degree of dissociation '$\alpha$' for weak acid=$\sqrt{\frac{K_a}{C}}$

For $0.1Mm-nitrobenzoicacid$

${\alpha }_1=\sqrt{\frac{K_a}{C}}=\sqrt{\frac{36\times {10}^{-5}}{C}}$

For $0.1Maceticacid$

${\alpha }_2=\sqrt{\frac{K_a}{C}}=\sqrt{\frac{1.8\times {10}^{-5}}{C}}$

$\frac{{\alpha }_1}{{\alpha }_2}=\frac{\sqrt{K_{a1}}}{\sqrt{K_{a2}}}=4.47$