Chemical and Ionic Equilibrium 2 Question 52
52. The dissociation constant of a substituted benzoic acid at $25^{\circ} \mathrm{C}$ is $1.0 \times 10^{-4}$. The $\mathrm{pH}$ of $0.01 \mathrm{M}$ solution of its sodium salt is
(2009)
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Solution:
- The hydrolysis reaction is
$$ \begin{gathered} A^{-}+\mathrm{H}{2} \mathrm{O} \rightleftharpoons A \mathrm{H}+\mathrm{OH}^{-} \ K{h}=\frac{K_{w}}{K_{a}}=10^{-10} \ {\left[\mathrm{OH}^{-}\right]=\sqrt{K_{h} C}=10^{-6}} \ \mathrm{pOH}=6 \quad \text { and } \quad \mathrm{pH}=8 \end{gathered} $$
