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WAEC Chemistry 2023 Paper

Question : 3

Total: 50

Which of the following reactions represents the hydrolysis of an alkanoate?

$\mathrm{CH}_3\mathrm{COOH} + \mathrm{OH}^{-} \rightleftharpoons \mathrm{H}^{+} \rightleftharpoons \mathrm{CH}_3\mathrm{COO}^{-} + \mathrm{H}_2\mathrm{O}$
$\mathrm{CH}_3\mathrm{COOH} + \mathrm{C}_2\mathrm{H}_5\mathrm{OH} \rightleftharpoons \mathrm{H}^{+} \rightleftharpoons \mathrm{CH}_3\mathrm{COOC}_2\mathrm{H}_5 + \mathrm{H}_2\mathrm{O}$
$\mathrm{CH}_3\mathrm{COOC} \mathrm{CO}_5 + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{H}^{+} \rightleftharpoons \mathrm{CH}_3\mathrm{COO}^{-} + \mathrm{CH}_3\mathrm{CH}_2\mathrm{OH}$
$\mathrm{CH}_3\mathrm{COOCH}_2\mathrm{CH}_3 + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{H}^{+} \rightleftharpoons \mathrm{CH}_3\mathrm{COOH} + \mathrm{CH}_3\mathrm{CH}_2\mathrm{OH}$

Solution:

Concept:

Hydrolysis of an alkanoate (ester) is the splitting of the ester by water to produce a carboxylic acid and an alcohol.

Explanation:

An alkanoate contains the functional group

-\mathrm{COO}-

In acidic hydrolysis, water breaks the ester bond.

The general equation is:

\mathrm{RCOOR'} + \mathrm{H}_2\mathrm{O} \xrightarrow{\mathrm{H}^+} \mathrm{RCOOH} + \mathrm{R'OH}

Here, ethyl ethanoate

\mathrm{CH}_3\mathrm{COOCH}_2\mathrm{CH}_3

reacts with water to form ethanoic acid

\mathrm{CH}_3\mathrm{COOH}

and ethanol

\mathrm{CH}_3\mathrm{CH}_2\mathrm{OH}

Thus, the reaction in option D matches this hydrolysis process.

Answer:

\mathrm{CH}_3\mathrm{COOCH}_2\mathrm{CH}_3 + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{H}^{+} \rightleftharpoons \mathrm{CH}_3\mathrm{COOH} + \mathrm{CH}_3\mathrm{CH}_2\mathrm{OH}

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