Question

The $pH$ of $0.01M$ solution of sodium salt of a substituted benzoic acid at ${25}^{o}C$ is: ($K_a=1.0\times {10}^{-4}$ at ${25}^{o}C$)

• A. $6$
• B. $8$
• C. $10$
• D. $12$

Answer 1

The correct option is B $8$

$\underset{c(1-h)}{ArCOONa}+H_{2}O\rightleftharpoons \underset{ch}{ArCOOH}+\underset{ch}{NaOH}$

$\therefore \left[{OH}^{-}\right]=ch=c\sqrt{\frac{K_H}{c}}=\sqrt{\frac{K_w\cdot c}{K_a}}=\sqrt{\frac{{10}^{-14}\times 0.01}{{10}^{-4}}}={10}^{-6}$

$[Note:h=\sqrt[]{\frac{K_H}{c}}=\sqrt{\frac{{10}^{-14}\times 0.01}{{10}^{-4}}}={10}^{-4}]$

$\therefore 1-h\simeq 1$

$\therefore$ $pOH=6$ and $pH=8$