AS Chemistry: Alcohols — Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Alcohols revision notes, covering classification, oxidation, dehydration and the distinguishing tests for Cambridge AS & A Level Chemistry 9701.

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Questions

1. Classify propan-1-ol, propan-2-ol and 2-methylpropan-2-ol as primary, secondary or tertiary, explaining the basis of the classification. [4]

2. Explain why ethanol has a much higher boiling point than propane, despite similar relative molecular masses. [3]

3. Propan-1-ol is oxidised with acidified potassium dichromate(VI).

(a) State the product and conditions if you distil. [2] (b) State the product and conditions if you reflux. [2] (c) State the colour change observed. [1] (d) State what happens if 2-methylpropan-2-ol is treated the same way, and explain. [2]

4. Ethanol can be dehydrated to ethene.

(a) State a suitable reagent and the conditions for this dehydration. [2] (b) Name the type of reaction. [1]

5. Describe the iodoform (tri-iodomethane) test.

(a) State the reagents. [1] (b) State the positive observation. [1] (c) State which structural feature gives a positive result. [2]

6. Ethanol can be prepared from ethanal, from ethanoic acid or from ethyl ethanoate.

(a) State a reagent for converting ethanal into ethanol, and write an equation for the reaction, using [H] to represent the reducing agent. [2] (b) State the only one of the two common hydride reducing agents that can convert ethanoic acid into ethanol, and write an equation for the reaction, using [H]. [2] (c) State the reagents and conditions for obtaining ethanol from ethyl ethanoate, and name the other product formed when an alkali is used. [2]

7. Ethanol is added separately to (i) a small piece of sodium and (ii) phosphorus(V) chloride (PCl₅).

(a) State the observation in each case. [2] (b) Write an equation for the reaction with sodium. [1] (c) Explain why the reaction with PCl₅ is used as a test for the -OH group. [1]

8. Ethanol reacts with ethanoic acid in the presence of a small amount of concentrated sulfuric acid.

(a) Name the type of reaction and the organic product. [2] (b) State the role of the concentrated sulfuric acid. [1]

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9. Propanoic acid, CH₃CH₂COOH, is reduced to propan-1-ol by LiAlH₄. Write an equation for this reaction, using [H] to represent the reducing agent. [2]

Answers

1. Primary — the carbon bearing the OH is attached to one other carbon: propan-1-ol [1]. Secondary — attached to two: propan-2-ol [1]. Tertiary — attached to three: 2-methylpropan-2-ol [1]. The classification depends on the number of alkyl groups on the carbon carrying the OH group [1].

2. Ethanol molecules form hydrogen bonds with each other [1] because O–H is present [1]; propane has only weak instantaneous dipole–induced dipole forces, so far less energy is needed to separate its molecules [1].

3. (a) Propanal; K₂Cr₂O₇/H₂SO₄, warm and distil off the product as it forms [1] [1]. (b) Propanoic acid; K₂Cr₂O₇/H₂SO₄, heat under reflux [1] [1]. (c) Orange to green [1]. (d) No reaction / no colour change [1], because a tertiary alcohol has no hydrogen on the carbon bearing the OH group, so it cannot be oxidised without breaking a C–C bond [1].

4. (a) Any one route, reagent and matching condition: concentrated sulfuric acid [1], heated to about 170 °C [1]; or an aluminium oxide (Al₂O₃) catalyst [1], with ethanol vapour passed over the heated catalyst at about 300–400 °C [1]. Maximum 2; the condition mark is awarded only with its own reagent (170 °C with Al₂O₃ scores the reagent mark only). (b) Elimination (dehydration) [1].

5. (a) Iodine and sodium hydroxide (alkaline aqueous iodine) [1]. (b) A pale yellow precipitate with an antiseptic smell [1]. (c) A CH₃CH(OH)– group, in an alcohol [1]; and a CH₃CO– group, in a carbonyl compound [1].

6. (a) NaBH₄ (or LiAlH₄) [1]; CH₃CHO + 2[H] → CH₃CH₂OH [1]. (b) LiAlH₄ (NaBH₄ is not a powerful enough reducing agent) [1]; CH₃COOH + 4[H] → CH₃CH₂OH + H₂O [1]. (c) Heat with dilute acid (e.g. dilute H₂SO₄) or dilute alkali (e.g. NaOH(aq)) — hydrolysis [1]; with NaOH(aq) the other product is sodium ethanoate, CH₃COONa (accept the ethanoate ion) [1].

7. (a) With sodium: effervescence (bubbles of gas) as the sodium reacts and gradually disappears [1]. With PCl₅: misty/steamy white fumes (of HCl) are produced [1]. (b) 2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂ [1]. (c) PCl₅ substitutes the hydroxyl group, replacing –OH with –Cl to give a chloroalkane [1], and HCl gas is released as a by-product, which fumes visibly (misty/steamy white fumes) on contact with moist air — so the appearance of these fumes shows that an –OH group was present and has reacted.

8. (a) Esterification (condensation) [1]; the product is ethyl ethanoate [1]. (b) It acts as a catalyst for the reaction [1].

9. CH₃CH₂COOH + 4[H] → CH₃CH₂CH₂OH + H₂O. Correct formula of propan-1-ol [1]; balanced with 4[H] and H₂O [1].

Examiner insight (June 2025): common errors were copying the formula of propan-1-ol incorrectly and equations that did not balance the hydrogen atoms. Count H and O on each side. Try the real question next: Cambridge International AS & A Level Chemistry 9701, June 2025, Paper 22, Question 4.

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Where marks are usually lost

• Confusing distil with reflux, so the aldehyde over-oxidises.
• Saying tertiary alcohols “react slowly” — they do not react at all under these conditions.
• Giving only one product for the iodoform-positive structural feature.
• Using NaBH₄ to reduce a carboxylic acid — only LiAlH₄ is a powerful enough reducing agent.
• Forgetting to balance the sodium/alcohol equation — two moles of alcohol react with two moles of sodium to produce one mole of hydrogen gas.
• Describing the PCl₅ test result as “bubbles” rather than the distinctive misty/steamy white fumes of HCl gas.
• Naming the ester product the wrong way round, or forgetting that concentrated sulfuric acid here is acting purely as a catalyst rather than being consumed in the reaction.

The full set of alcohol reactions, in one place

Beyond oxidation, an alcohol’s -OH group takes part in several other reaction types worth holding together as a set: with sodium, it behaves as a weakly acidic O-H group, releasing hydrogen gas and forming a sodium alkoxide; with concentrated sulfuric acid at about 170°C, or as vapour over a heated Al₂O₃ catalyst, it undergoes elimination (dehydration) to form an alkene; with a carboxylic acid and an acid catalyst, it undergoes condensation (esterification) to form an ester; and with PCl₅, it substitutes the -OH for chlorine, producing the characteristic misty fumes used as a simple confirmatory test for the -OH group in an unknown compound. For the full reaction scheme and oxidation-product table by alcohol class, see the Alcohols revision notes.