A neutral organic compound X (molecular formula C₂H₆O) on reacting with acidified K₂Cr₂O₇ forms another organic compound Y whose nature is acidic. X and Y on heating in the presence of conc. H₂SO₄ give a sweet smelling compound Z.
Generated by claude-sonnet-4-6 · 2026-06-15 06:48 · grounding rag
Model Answer
(i) Identification:
- X = Ethanol (C₂H₅OH) — neutral alcohol
- Y = Ethanoic acid (CH₃COOH) — acidic compound
- Z = Ethyl ethanoate (CH₃COOC₂H₅) — sweet-smelling ester
(ii) Chemical equations:
(1) X to Y (Oxidation):
$$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{acidified K}_2\text{Cr}_2\text{O}_7} \text{CH}_3\text{COOH}$$
(2) X to Z (Esterification):
$$\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{conc. H}_2\text{SO}_4, \Delta} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}$$
(iii) Roles:
(1) Acidified K₂Cr₂O₇ acts as an oxidising agent — it oxidises ethanol to ethanoic acid.
(2) Conc. H₂SO₄ acts as a dehydrating agent / catalyst — it removes water and drives the esterification forward.
(iv) The reaction of ester Z with an alkali is called Saponification (alkaline hydrolysis of ester).
Source: Carbon and its Compounds, sections 4.2.3, 4.2.5
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Explanation
- The key chain: ethanol → (oxidation) → ethanoic acid → (esterification with ethanol) → ethyl ethanoate.
- CBSE expects the role words: "oxidising agent" and "dehydrating agent/catalyst" — one word each earns the mark.
- "Saponification" is the specific term examiners look for in (iv); writing only "hydrolysis" may lose the mark.
- Balance equations properly; the esterification arrow must show conc. H₂SO₄ and heat (Δ) as conditions, not reactants.