Science (086) — CBSE Class 10 board question

(i) Ethanol → Ethene
$$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{conc. H}_2\text{SO}_4,\ 443\text{ K}} \text{CH}_2=\text{CH}_2 + \text{H}_2\text{O}$$
Condition: Excess conc. H₂SO₄ at 443 K (dehydration).

(ii) Ethene → Ethane
$$\text{CH}_2=\text{CH}_2 + \text{H}_2 \xrightarrow{\text{Ni, heat}} \text{CH}_3\text{CH}_3$$
Condition: Hydrogen gas in presence of Ni catalyst and heat (hydrogenation / addition reaction).

(iii) Ethane → Chloroethane
$$\text{CH}_3\text{CH}_3 + \text{Cl}_2 \xrightarrow{\text{sunlight}} \text{CH}_3\text{CH}_2\text{Cl} + \text{HCl}$$
Condition: Presence of sunlight (substitution reaction).

(iv) Ethanol → Ethanoic acid
$$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{alkaline KMnO}_4 \text{ or acidified K}_2\text{Cr}_2\text{O}_7} \text{CH}_3\text{COOH}$$
Condition: Oxidation using alkaline KMnO₄ or acidified K₂Cr₂O₇.

(v) Ethanoic acid → Ethyl ethanoate
$$\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{conc. H}_2\text{SO}_4,\ \Delta} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}$$
Condition: Conc. H₂SO₄ as catalyst and heat (esterification reaction).

Source: Chapter 4, Sections 4.3.2, 4.3.3, 4.3.4

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• Each conversion must have: balanced equation + condition — both are needed for full marks.
• (i) is dehydration (elimination); (ii) is addition/hydrogenation; (iii) is substitution (sunlight is the key condition); (iv) is oxidation — either oxidising agent is acceptable; (v) is esterification — the product is an ester and the reaction is reversible (shown by ⇌ in some texts).
• Examiners award 1 mark per conversion, split between the equation and the stated condition. Missing the condition loses the mark even if the equation is correct.