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2025 O Level Chem P1 Q37 — Organic Chemistry / Ethanol Solution

Organic Chemistry / Ethanol 2025 O Level Pure Chemistry · Paper 1 · Q37

Question

Three statements about ethanol are listed. 1 When ethanol is made by the fermentation of glucose, a larger molecule is broken down to form smaller molecules. 2 When ethanol is made by the reaction between steam and ethene, a substitution reaction takes place. 3 When ethanol is oxidised by atmospheric oxygen at room temperature, an organic compound is formed which may then react with sodium to form a gas. Which statements are correct?

A1, 2 and 3
B1 and 2 only
C1 and 3 only
D2 and 3 only

Correct answer: C

Video Solution

Explanation

Answer: C. Check each statement.

Statement 1 (fermentation breaks down glucose): correct. \(\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2\) — one larger molecule (glucose) breaks into two smaller ones.

Statement 2 (steam + ethene is a substitution reaction): wrong. \(\text{C}_2\text{H}_4 + \text{H}_2\text{O} \rightarrow \text{C}_2\text{H}_5\text{OH}\) is an addition reaction across the C=C double bond — nothing is replaced.

Statement 3 (ethanol oxidised in air, product reacts with sodium to give gas): correct. Slow oxidation of ethanol gives ethanoic acid \(\text{CH}_3\text{COOH}\), which reacts with sodium: \(2\text{CH}_3\text{COOH} + 2\text{Na} \rightarrow 2\text{CH}_3\text{COONa} + \text{H}_2(\text{g})\).

Statements 1 and 3 correct → option C.

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