Question

You are titrating a solution of ethanoic acid, $C{H}_{3}COOH\left(aq\right)$ (acetic acid), with aqueous sodium hydroxide, to a phenolphthalein endpoint. Ethanoic acid is a weak acid.
Which of the following statement BEST describes the principal species (other than water) that are present in solution at the equivalence point of your titration?

• A. Equal quantities of $N{a}^{+}\left(aq\right)$ and $C{H}_{3}CO{O}^{-}\left(aq\right)$.
• B. Equal quantities of $N{a}^{+}\left(aq\right)$ and $C{H}_{3}CO{O}^{-}\left(aq\right)$, plus a small quantity of $O{H}^{-}$
• C. A significant quantity of $N{a}^{+}\left(aq\right)$, along with somewhat smaller quantities of $C{H}_{3}COOH\left(aq\right)$ and $C{H}_{3}CO{O}^{-}\left(aq\right)$, plus a trace of $O{H}^{-}$.
• D. Equal quantities of $N{a}^{+}\left(aq\right),C{H}_{3}CO{O}^{-}\left(aq\right)$, and $O{H}^{-}$.

Answer 1

The correct option is B Equal quantities of $N{a}^{+}\left(aq\right)$ and $C{H}_{3}CO{O}^{-}\left(aq\right)$, plus a small quantity of $O{H}^{-}$

During a weak acid titration with strong base following reactions takes place at equivalence point.

$C{H}_{3}COOH\left(aq\right)+NaOH\to C{H}_{3}COONa+H_{2}O$

$C{H}_{3}COONa+H_{2}O\to C{H}_{3}CO{O}^{-}\left(aq\right)+N{a}^{+}\left(aq\right)+O{H}^{-}$

Here we found small quantity of $O{H}^{-}$ because $NaOH$ is a strong base and at equivalence point the solution remains slightly basic with equal ions of $N{a}^{+}$ and $C{H}_{3}CO{O}^{-}$

Option B is correct.