AQA A-Level Chemistry: Alcohols (7405) – 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 from your board or school.

These questions cover section 3.3.5 Alcohols of the AQA AS and A-level Chemistry specification (7404/7405), version 1.2, July 2026, for AS and A-level exams June 2016 onwards: 3.3.5.1 to 3.3.5.3 and Required practical 5. All of it is AS content, so nothing here is A-level only. The topic is examined on Paper 2 at AS and A-level, and A-level Paper 3 can test any content.

Learn the ideas first in the alcohols study guide and the alcohols revision notes. The course hub is AQA A-Level Chemistry, and the printable checklist lists every specification point. Use Ar values C = 12.0, H = 1.0, O = 16.0.

Questions

1. Classify each alcohol as primary, secondary or tertiary.

(a) pentan-2-ol [1] (b) 3-methylpentan-3-ol [1] (c) 2,2-dimethylpropan-1-ol [1]

2. Explain the meaning of the term biofuel, and state why ethanol made by hydrating ethene from crude oil is not a biofuel. [2]

3. Ethanol is produced industrially by fermentation.

(a) Write an equation for the fermentation of glucose. [1] (b) Justify the temperature used. [2] (c) Explain why air is kept out of the fermentation vessel. [1] (d) State how the ethanol is separated from the mixture. [1]

4. A brewer wants 115 g of ethanol by fermentation.

(a) Calculate the minimum mass of glucose needed. [2] (b) Calculate the mass of carbon dioxide released. [1]

5. Ethanol from sugar cane is sometimes described as carbon neutral.

(a) Write equations for photosynthesis, fermentation and the complete combustion of ethanol. [3] (b) Use your equations to show why the fuel can be described as carbon neutral. [1] (c) Give two reasons why the statement is not valid. [2]

6. 2-methylpropene reacts with steam in the presence of an acid catalyst.

(a) Outline the mechanism for the formation of the major product. [4] (b) Name the minor product and explain why less of it forms. [2]

7. Propan-1-ol is oxidised by acidified potassium dichromate(VI).

(a) Write an equation, using [O], for the formation of propanal. [1] (b) Write an equation, using [O], for the formation of propanoic acid from propan-1-ol. [1] (c) Explain how the method is chosen to obtain propanal rather than propanoic acid. [3] (d) State the colour change in the reaction mixture. [1]

8. Describe a test to distinguish butanal from butanone. Give the reagent, the condition and what is seen with each compound, and write an equation, using [O], for the reaction of butanal. [4]

9. Pentan-3-ol is heated with an acid catalyst.

(a) Name a suitable acid catalyst. [1] (b) Outline the mechanism for the elimination of water from pentan-3-ol. [3] (c) Name the products and explain why there is more than one. [2]

10. In Required practical 5, a student makes cyclohexene from cyclohexanol and purifies it.

(a) The distillate is shaken with sodium carbonate solution in a separating funnel. Explain why, and why the tap must be opened often. [2] (b) Name a drying agent and state how you can tell the cyclohexene is dry. [2] (c) 12.5 g of cyclohexanol (Mr 100.0) gives 7.38 g of cyclohexene (Mr 82.0). Calculate the percentage yield. [3]

11. P, Q and R are isomers with formula C₄H₁₀O. Each is warmed with acidified potassium dichromate(VI).

• P turns the mixture green. When the product is distilled off, it gives a silver mirror with Tollens’ reagent. Elimination of P gives but-1-ene only.
• Q turns the mixture green. The product does not react with Tollens’ reagent. Elimination of Q gives three alkenes.
• R leaves the mixture orange. Elimination of R gives 2-methylpropene only.

(a) Identify P, Q and R, giving one reason for each. [6] (b) The equation for the oxidation of Q is Cr₂O₇²⁻ + 8H⁺ + 3C₄H₁₀O → 2Cr³⁺ + 3C₄H₈O + 7H₂O. Calculate the volume of 0.0500 mol dm⁻³ potassium dichromate(VI) that reacts with 0.370 g of Q. [3]

12. A company plans to make poly(ethene) from sugar cane instead of crude oil.

(a) Outline the three stages from glucose to poly(ethene), giving the reagent or condition for each stage. [3] (b) Discuss the environmental and ethical issues the company should consider. [4]

Answers

1. (a) Secondary [1] (b) Tertiary [1] (c) Primary: the C–OH carbon is joined to one other carbon [1] Examiner insight: Classification depends only on the carbon bonded to –OH; counting all branches in the molecule gives the wrong class.

2. A biofuel is made from biological material (biomass) that has been grown recently and can be regrown [1]. Ethene from crude oil comes from a finite fossil source, not recent biomass [1]. [2] Examiner insight: “Renewable” alone may not score; tie the fuel to recently grown biological material.

3. (a) C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ [1] (b) About 35 °C: a lower temperature gives a slow rate [1]; a higher temperature denatures the enzymes in yeast [1] (c) Oxygen would oxidise ethanol to ethanoic acid (or yeast would respire aerobically) [1] (d) Fractional distillation [1] Examiner insight: For (b) both sides of the compromise are needed; “optimum temperature for yeast” alone earns at most one mark.

4. (a) n(ethanol) = 115 ÷ 46.0 = 2.50 mol, so n(glucose) = 1.25 mol [1]; mass = 1.25 × 180.0 = 225 g [1] (b) n(CO₂) = 2.50 mol; mass = 2.50 × 44.0 = 110 g [1] Examiner insight: Set out each mole step, including the 1 : 2 ratio, so the method in (b) is clear even if (a) contains a slip.

5. (a) 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ [1]; C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ [1]; C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O [1] (b) 6 mol CO₂ absorbed; 2 mol from fermentation and 4 mol from burning 2 mol ethanol are released, so no net CO₂ [1] (c) Any two: fossil fuels used for farm machinery [1]; making fertiliser [1]; powering distillation; transport. [6] Examiner insight: In (b) the combustion equation must be doubled (or the counting must allow for 2 mol ethanol); comparing 6 with 4 loses the mark.

6. (a) Arrow from the C=C bond to H⁺ (or to H of H₃O⁺) [1]; tertiary carbocation (CH₃)₃C⁺ drawn [1]; arrow from a lone pair on the O of H₂O to C⁺ [1]; loss of H⁺ from (CH₃)₃C–OH₂⁺ to give 2-methylpropan-2-ol [1] (b) 2-methylpropan-1-ol [1]; it forms through a primary carbocation, which is less stable than the tertiary one [1] Examiner insight: Arrows must start at a bond or a lone pair; an arrow starting from the H⁺ ion or from a charge is not credited.

7. (a) CH₃CH₂CH₂OH + [O] → CH₃CH₂CHO + H₂O [1] (b) CH₃CH₂CH₂OH + 2[O] → CH₃CH₂COOH + H₂O [1] (c) Use excess propan-1-ol (limited oxidising agent) with gentle heat [1]; distil the propanal off as it forms [1]; propanal has a lower boiling point (no hydrogen bonding between its molecules), so it leaves before it is oxidised to the acid [1] (d) Orange to green [1] Examiner insight: “Distil” without the reason it prevents further oxidation usually scores only one of the three marks in (c).

8. Tollens’ reagent, warmed in a water bath [1]; butanal gives a silver mirror [1]; butanone shows no change [1]; CH₃CH₂CH₂CHO + [O] → CH₃CH₂CH₂COOH [1]. (Fehling’s: butanal gives a red precipitate, butanone stays blue.) [4] Examiner insight: An observation must be given for both compounds; “no reaction” for butanone needs to be stated, not implied.

9. (a) Concentrated sulfuric acid or concentrated phosphoric acid [1] (b) Lone pair on O attacks H⁺ to give the protonated alcohol [1]; C–O bond breaks and water leaves, giving the carbocation on C3 [1]; C–H bond electrons on C2 form C=C and H⁺ is lost [1] (c) (E)-pent-2-ene and (Z)-pent-2-ene [1]; C2 and C4 are equivalent so only pent-2-ene forms, but rotation about C=C is restricted and each carbon of the double bond has two different groups [1] Examiner insight: “Pentene” without the position and E/Z labels is not a name and does not score.

10. (a) To neutralise (remove) acid carried over in the distillate [1]; carbon dioxide forms and pressure builds up [1] (b) Anhydrous calcium chloride or magnesium sulfate [1]; the liquid turns from cloudy to clear [1] (c) n(cyclohexanol) = 12.5 ÷ 100.0 = 0.125 mol [1]; n(cyclohexene) = 7.38 ÷ 82.0 = 0.0900 mol [1]; yield = 0.0900 ÷ 0.125 × 100 = 72.0 % [1] Examiner insight: Comparing masses (7.38 ÷ 12.5) instead of moles gives 59.0 % and loses the method marks; always convert both to moles.

11. (a) P is butan-1-ol [1]: oxidised to an aldehyde, so primary, and an unbranched chain gives but-1-ene [1]. Q is butan-2-ol [1]: oxidised to a ketone, so secondary; three alkenes are but-1-ene and E/Z but-2-ene [1]. R is 2-methylpropan-2-ol [1]: not oxidised, so tertiary, and it gives 2-methylpropene [1] (b) n(Q) = 0.370 ÷ 74.0 = 5.00 × 10⁻³ mol [1]; n(Cr₂O₇²⁻) = 5.00 × 10⁻³ ÷ 3 = 1.667 × 10⁻³ mol [1]; volume = 1.667 × 10⁻³ ÷ 0.0500 × 1000 = 33.3 cm³ [1] Examiner insight: Each identification needs evidence from the data; a correct name with no reason gets only the name mark.

12. (a) Fermentation of glucose with yeast, about 35 °C, no air [1]; ethanol (after fractional distillation) heated with concentrated phosphoric or sulfuric acid to give ethene [1]; addition polymerisation of ethene to poly(ethene) [1] (b) Any four: sugar cane is renewable [1]; less use of finite crude oil [1]; land used for fuel crops is not used for food and may raise food prices [1]; clearing forest destroys habitats and releases CO₂ [1]; fertiliser run-off; fossil-fuel energy is still used in farming and distillation. [7] Examiner insight: “Discuss” expects points on both sides; four advantages with no drawbacks will not reach full marks.

Where marks are usually lost

• Leaving yeast or “no air” out of the fermentation conditions.
• Counting 4 mol CO₂ from combustion against 6 absorbed without doubling for 2 mol ethanol.
• Curly arrows starting from H⁺ or from a positive charge.
• Forgetting that H⁺ is regenerated in hydration and elimination.
• Writing “reflux” for making an aldehyde.
• Missing the “no change” observation for the ketone.
• Missing E/Z isomers in elimination products.
• Using masses instead of moles in percentage yield.
• Using a 1 : 1 ratio for dichromate and alcohol instead of the 1 : 3 ratio in the equation.

Next steps

• Alcohols revision notes
• Alcohols study guide
• AQA A-Level Chemistry alkenes
• AQA A-Level Chemistry exam preparation
• AQA A-Level Chemistry hub
• Printable checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

AQA, AS and A-level Chemistry specification (7404/7405), version 1.2, July 2026, for AS and A-level exams June 2016 onwards: section 3.3.5 Alcohols (3.3.5.1 to 3.3.5.3), with Required practical 5.