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Carbon and its Compounds — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceCarbon and its Compounds5 Marks
Question
A compound C (molecular formula, $C _2 H _4 O _2$ ) reacts with Na -metal to form a compound $R$ and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol A in presence of an acid forms a sweet smelling compound S (molecular formula, $C _3 H _6 O _2$ ). On addition of NaOH to C , it also gives R and water. S on treatment with NaOH solution gives back R and A .Identify $C , R , A , S$ and write down the reactions involved.
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Answer

Compound C with molecular formula $C _2 H _4 O _2$ contains two oxygen atoms so it can be either ester or carboxylic acid. Since it reacts with sodium metal to form compound R and evolves a gas which burns with pop sound, therefore it should be a carboxylic acid which forms sodium alkanoate and hydrogen gas with sodium metal.
$2 CH_3 COOH+2 Na \longrightarrow 2 CH_3 COONa+H_2 \uparrow$
The gas which burns with pop sound is hydrogen gas.
Reaction of ethanoic acid with alcohol in the presence of an acid (Conc. $H _2 SO _4$ ) forms sweet smelling ester. So compound S that is formed due to reaction of ethanoic acid and methanol $(A)$ is methyl ethanoate with molecular formula $C _3 H _6 O _2$ and structural formula $CH _3 COOCH _3$.
$CH_3 COOH+CH_3 OH \xrightarrow{\text { Conc. } H_2 So_4} CH_3 COOCH_3+H_2 O$
Hence compound $C =$ Ethanoic acid $\left( CH _3 COOH \right), R =$ Sodium ethanoate $\left( CH _3 COONa \right), A =$ Methanol $\left( CH _3 OH \right)$ and $S =$ Methyl merhanoate $\left( CH _3 COOCH _3\right)$

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