WAEC Chemistry 2020 Paper

Concept:Compounds having a hydrogen atom bonded to oxygen, such as carboxylic acids and alcohols, can release hydrogen gas when treated with sodium metal.Explanation:I. $\mathrm{CH_3COOH}$ is ethanoic acid, a carboxylic acid.It contains an acidic hydrogen attached to oxygen.This hydrogen is replaced by sodium, releasing hydrogen gas:$$2\mathrm{CH_3COOH} + 2\mathrm{Na} \rightarrow 2\mathrm{CH_3COONa} + \mathrm{H_2}$$So compound I releases hydrogen.II. $\mathrm{CH_3CH_2OH}$ is ethanol, an alcohol.It has a hydroxyl group, so its hydrogen attached to oxygen is reactive toward sodium.The reaction is:$$2\mathrm{CH_3CH_2OH} + 2\mathrm{Na} \rightarrow 2\mathrm{CH_3CH_2ONa} + \mathrm{H_2}$$Thus compound II also releases hydrogen.III. $\mathrm{CH_3COOCH_3}$ is an ester.It has no hydrogen atom directly attached to oxygen in a replaceable form.Therefore, it does not react with sodium metal to release hydrogen gas.Answer:B. I and II only