(a) An acid X reacts with an alcohol Y in the presence of a catalyst acid to form a substance Z that has a pleasant smell. Identify X, Y and Z. Write the chemical equation for the reaction involved and name it, giving justification for the name. The substance Z on reacting with sodium hydroxide gives back alcohol Y and sodium ethanoate. Write the chemical equation for the reaction involved.
Generated by claude-sonnet-4-6 · 2026-06-15 06:48 · grounding rag
Model Answer
Identification:
- X = Ethanoic acid (CH₃COOH)
- Y = Ethanol (C₂H₅OH)
- Z = Ethyl ethanoate (CH₃COOC₂H₅) — an ester with a pleasant smell
Reaction 1 — Esterification:
$$\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \underset{\Delta}{\overset{\text{Conc. H}_2\text{SO}_4}{\rightleftharpoons}} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}$$
Name: Esterification reaction.
Justification: When a carboxylic acid reacts with an alcohol in the presence of an acid catalyst, an ester (Z) is formed. Since an ester is the product, the reaction is called esterification.
Reaction 2 — Saponification (hydrolysis of ester with NaOH):
$$\text{CH}_3\text{COOC}_2\text{H}_5 + \text{NaOH} \rightarrow \text{CH}_3\text{COONa} + \text{C}_2\text{H}_5\text{OH}$$
Ethyl ethanoate reacts with sodium hydroxide to give sodium ethanoate and ethanol (alcohol Y is recovered).
Source: Chapter 4 — Carbon and its Compounds, Section 4.4.2 (Ethanoic Acid — Reactions)
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Explanation
- X, Y, Z identification carries 1 mark — name all three clearly.
- Esterification equation carries ~1–1.5 marks — include catalyst (conc. H₂SO₄), heat, and the reversible arrow (⇌).
- Naming + justification carries ~1 mark — state that ester is formed, hence "esterification."
- Saponification equation carries ~1 mark — this reverse reaction is called saponification; the equation must show recovery of ethanol (Y) and formation of sodium ethanoate.
- Do not confuse saponification (ester + NaOH) with hydrolysis by water; in board exams always write the NaOH equation here.