Practise 36 real questions on Hydrocarbons from 2021 to 2026. See the answer and explanation as soon as you answer.
Hydrocarbons is one of the 18 main topics in our A Level Chemistry (Cambridge (CAIE) 9701) question bank, and about 6% of its real questions come from it. Tayyari Karo has 36 real questions on this topic from 2021 to 2026, from Paper 1, Paper 2, Paper 4; 26 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 20 hard, 13 medium, 3 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
Which compound will decolourise Br2(aq) in the dark?
Answer: C. CH3CH=CHCH2CH2CH2OH
Only the alkene undergoes electrophilic addition with bromine water in the dark.
The structural formula of hept-1,4,5-triene is CH2=CH-CH2-CH=C=CH-CH3. How many of the carbon atoms in one molecule of hept-1,4,5-triene are sp2 hybridised?
Answer: A. 4
Carbons in a C=C double bond are normally sp2, but the central carbon of the cumulated diene (C=C=C, at C5) is sp hybridised, not sp2; only C1, C2, C4 and C6 are sp2 hybridised, giving 4.
The fumes from petrol-burning car exhausts contain: 1 unburnt hydrocarbons, 2 nitrogen dioxide, 3 carbon monoxide. Which pollutants are removed by oxidation in a catalytic converter?
Answer: C. 1 and 3 only
In a catalytic converter, unburnt hydrocarbons and carbon monoxide are removed by oxidation (to CO2 and H2O); nitrogen dioxide/oxides are removed by reduction (to N2), not oxidation.
Which equation represents a reaction that proceeds through initiation, propagation and termination steps?
Answer: A. C4H10 + Cl2 → C4H9Cl + HCl
Free-radical substitution of an alkane by chlorine (initiated by UV light, homolytic fission) proceeds via initiation, propagation and termination steps; the other reactions are ionic/nucleophilic mechanisms.
The hydrocarbon C17H36 can be cracked. Which compound is the least likely to be produced in this reaction?
Answer: D. C16H34
Cracking C17H36 breaks it into smaller fragments; a product with 16 carbons (C16H34) is far too close to the original chain length to be a plausible cracking product, unlike the smaller alkane/alkene fragments in A–C.
Which compound would produce two different carboxylic acids when treated with hot, concentrated, acidified manganate(VII) ions? A: CH3CH=C(CH3)CH(CH3)2; B: CH3CH=CHCH(CH3)2; C: cyclohexene; D: (CH3)2CHCH=CHCH(CH3)2
Answer: B. CH3CH=CHCH(CH3)2
In B both alkene carbons bear one H, so oxidative cleavage gives CH3COOH and (CH3)2CHCOOH (two different acids); A has a trisubstituted alkene carbon (gives a ketone), C is cyclic (gives one diacid), D is symmetric (gives two identical acids).
| Session | Paper 1 | Paper 2 | Paper 4 |
|---|---|---|---|
| May/June 2026 | 2 | 1 | – |
| May/June 2025 | 3 | – | 1 |
| October/November 2025 | 3 | 1 | 1 |
| May/June 2024 | 1 | 1 | 1 |
| October/November 2024 | 3 | – | – |
| May/June 2023 | 2 | – | – |
| October/November 2023 | 4 | 1 | – |
| May/June 2022 | 1 | – | – |
| October/November 2022 | – | – | 1 |
| May/June 2021 | 4 | 2 | – |
| October/November 2021 | 3 | – | – |
36 real A Level Chemistry (9701) questions on Hydrocarbons from 2021 to 2026, from Paper 1, Paper 2, Paper 4. Each one shows the year, session and paper it came from.
Yes. Every question shows the correct answer and a short explanation the moment you answer.
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