Question

$p{K}_a$ of acetic acid is 4.741. The concentration of $C{H}_{3}COONa$ is 0.01 M. The pH of $C{H}_{3}COONa$ is?

• A. $3.37$
• B. $4.37$
• C. $4.74$
• D. None of these

Answer 1

The correct option is C $4.74$

$C{H}_{3}COOH\rightleftharpoons C{H}_{3}CO{O}^{-}+H^{+}$

Given $p{K}_a=4.74$

$K_a={10}^{-4.74}=1.8\times {10}^{-5}$

$K_a=\frac{\left[H^{+}\right]\left[C{H}_{3}CO{O}^{-}\right]}{\left[C{H}_{3}COOH\right]}$

$\Rightarrow \left[H^{+}\right]=\frac{K_a\times \left[C{H}_{3}COOH\right]}{C{H}_{3}CO{O}^{-}}$

$=\frac{1.8\times {10}^{-5}\times 0.01}{0.01}$

$=1.8\times {10}^{-5}m$

$pH=-\log K_a$

$\Rightarrow pH=-\log (.8\times {10}^{-5})=4.74$ .