Question

If $NaOH$ is added to a solution of acetic acid:

• A. $H^{+}$ ions increases
• B. $pH$ decreases
• C. $\left[C{H}_{3}CO{O}^{-}\right]$ increases
• D. $\left[C{H}_{3}COOH\right]$ increases

Answer 1

Answer: (C)

$\left[C{H}_{3}CO{O}^{-}\right]$ increases

Acetic acid is a weak acid. Its dissociation equilibrium is as shown below.
$C{H}_{3}COOH\to C{H}_{3}CO{O}^{-}+H^{+}$

When sodium hydroxide is added into the solution, the hydroxide ions react with hydrogen ions to form water.

$H^{+}+O{H}^{-}\rightleftharpoons H_{2}O$.

Thus, the hydrogen ion concentration decreases and the $pH$ of the solution increases.

Hence, the equilibrium for the dissociation of acetic acid will shift towards right, this will increase the acetate ion concentration.

Option C is correct.