Compound 'A' is Ethanoic acid (CH₃COOH).
(i) Ethanoic acid; molecular formula C₂H₄O₂.
Structure:
$$\text{CH}_3 - \text{COOH}$$
(Carbon–carbon single bond, with —COOH as the carboxylic acid functional group.)
(ii) Chemical equation for esterification:
$$\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{conc. H}_2\text{SO}_4, \Delta} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}$$
Compound 'B' is ethyl ethanoate (an ester). Concentrated H₂SO₄ acts as a catalyst (and dehydrating agent), speeding up the reaction.
(iii) Compound 'A' (ethanoic acid) can be obtained back from 'B' by saponification — heating the ester 'B' with an acid (or alkali) and water (hydrolysis).
(iv) Ethanoic acid is obtained from ethanol by oxidation, using an oxidising agent such as alkaline KMnO₄ or acidified K₂Cr₂O₇.
$$\text{C}_2\text{H}_5\text{OH} \xrightarrow{[\text{O}]} \text{CH}_3\text{COOH}$$
(v) Carbon dioxide (CO₂) gas is produced when ethanoic acid reacts with washing soda (Na₂CO₃).
$$2\text{CH}_3\text{COOH} + \text{Na}_2\text{CO}_3 \rightarrow 2\text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2\uparrow$$
Source: Chapter 4, Section 4.4 — Some Important Carbon Compounds: Ethanol and Ethanoic Acid
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