Hydrocarbons — AS & A Level Chemistry (9701) questions by topic
Addition, substitution and oxidative-cleavage reactions run through this topic: classifying the reaction type when ethene forms ethanol with steam, identifying products of hot acidified potassium manganate(VII) oxidation, and deducing hydrocarbon structures from Mr and HBr addition data.
Identify, deduce, state, draw and explain lead 65 questions from 2023 to 2025 papers, worth 1 to 22 marks, the broadest mark range here, so single-mark recall sits next to full mechanism and isomer-counting answers. Submitting mechanism diagrams and isomer lists for instant marking catches a missing curly arrow from the C=C bond or an overlooked positional isomer before the same gap recurs across a whole hydrocarbons paper.
What examiners look for
- A recurring criticism is choosing B by overlooking the cis-trans geometrical isomers of but-2-ene.
- Examiners flag common mechanism errors: full charges shown on H-Br instead of a dipole, curly arrows starting from one end of the C=C bond rather than the bond itself, and intermediates drawn with both a negative charge and a partial negative charge.
- A common error used C3H7 rather than the unambiguous expanded (CH3)2CH- when drawing a structure.
- Strong scripts found the empirical formula CH2 from percentage hydrogen, used the 1:1 reaction with Br2 to reach Mr = 56, and correctly counted four structural alkenes.
- Candidates who explained that neither structure shows geometrical isomerism because one carbon of the C=C bond carries two identical groups scored the mark.
May–June 2025, Paper 11
An alkene P reacts with an excess of hot concentrated acidified KMnO4(aq). Methylpropanoic acid is the only organic product. What is alkene P? A 2,5-dimethylhex-3-ene B…
Answer this question and get it marked →Three substances are listed. 1 butane 2 hydrogen 3 hydrogen bromide Which substances are possible products of the free-radical substitution reaction between ethane and bromine? A…
Answer this question and get it marked →May–June 2025, Paper 12
Samples of the gases CH3Cl and Cl2 are mixed together and irradiated with ultraviolet light. Which compound is produced by a termination step in the reaction? A HCl B CH2=CH2 C…
Answer this question and get it marked →Propan-1-ol, C3H7OH, is dehydrated by passing its vapour over hot aluminium oxide to give a hydrocarbon. Which structural formula represents the product obtained when the…
Answer this question and get it marked →Alkane S has molecular formula C4H10. S reacts with Cl2(g) in the presence of sunlight to produce only two different monochloroalkanes, C4H9Cl. Both of these monochloroalkanes are…
Answer this question and get it marked →May–June 2025, Paper 13
Which row shows the products formed when cyclohexene reacts with acidified KMnO4 under different conditions? A cold dilute: cyclohexanediol; hot concentrated: hexanedioic acid B…
Answer this question and get it marked →Two steps in the free-radical substitution reaction between methane and chlorine are shown. step 1 CH3• + Cl2 → CH3Cl + Cl• step 2 CH3Cl + Cl• → CH2Cl• + HCl Which statement is…
Answer this question and get it marked →May–June 2025, Paper 14
When 0.010 mol of a hydrocarbon X reacts with 720 cm^3 of hydrogen at room conditions, an alkane is formed. What is hydrocarbon X? A A di-substituted benzene with two vinyl groups…
Answer this question and get it marked →An alkene reacts with hot concentrated acidified KMnO4 to produce a single organic product as shown: the product is a methyl ketone attached to a carboxylic acid chain. What is…
Answer this question and get it marked →May–June 2025, Paper 24
W has two positional isomers. Only one shows stereoisomerism. Draw the structures of the two positional isomers of W in the boxes.
Answer this question and get it marked →May–June 2025, Paper 41
A hydrocarbon is known to be either compound D or compound E. D is 1,2-diethylbenzene (a benzene ring with two CH2CH3 groups at positions 1 and 2). E is 1,3-diethylbenzene (a…
Answer this question and get it marked →Bromine reacts with methylbenzene in the dark in the presence of a suitable catalyst to form HBr and compound L, C7H7Br. L is one of three isomers that can form in this reaction.…
Answer this question and get it marked →May–June 2025, Paper 42
Benzene reacts with HNO3 and H2SO4 to form nitrobenzene. (i) Write an equation to show how the electrophile is formed from HNO3 and H2SO4. (ii) Complete the mechanism for the…
Answer this question and get it marked →May–June 2025, Paper 43
A hydrocarbon is known to be either compound D or compound E. D is 1,2-diethylbenzene (a benzene ring with two CH2CH3 groups at positions 1 and 2). E is 1,3-diethylbenzene (a…
Answer this question and get it marked →Bromine reacts with methylbenzene in the dark in the presence of a suitable catalyst to form HBr and compound L, C7H7Br. L is one of three isomers that can form in this reaction.…
Answer this question and get it marked →May–June 2024, Paper 11
The diagram shows the structure of X: a molecule NC-CH=CH2 (acrylonitrile / prop-2-enenitrile), drawn with the NC group and an H on one alkene carbon and two H atoms on the other.…
Answer this question and get it marked →Which reaction occurs when ethane and chlorine are mixed in diffused sunlight? A a free-radical substitution with hydrogen given off B a free-radical substitution with hydrogen…
Answer this question and get it marked →May–June 2024, Paper 12
Z is a gaseous hydrocarbon which has a density of 3.50 x 10^-3 g cm^-3 under room conditions. Z reacts with an excess of hot concentrated acidified KMnO4. Only one type of…
Answer this question and get it marked →The molecule of limonene, C10H16, contains a 6-membered ring. This is the only cyclic component in its structure. Which volume of hydrogen, at room conditions, is required to…
Answer this question and get it marked →May–June 2024, Paper 13
What is the correct name of the major product of the reaction of HBr with 3-ethylhex-3-ene? A 3-bromo-3-ethylhexane B 3-bromo-4-ethylhexane C 4-bromo-3-ethylhexane D…
Answer this question and get it marked →The alkane CH3CH2CH(CH3)2 undergoes free radical substitution with chlorine. No C-C bonds are broken in this reaction. How many isomeric products, including positional and optical…
Answer this question and get it marked →But-2-ene reacts with cold dilute acidified KMnO4 to give product X. But-2-ene reacts with an excess of hot concentrated acidified KMnO4 to give product Y. Which statement about X…
Answer this question and get it marked →May–June 2024, Paper 23
M reacts to form R by the addition of one reagent, as shown in Fig. 5.1. M is cyclohexene and R is cyclohexane-1,2-diol (a cyclohexane ring with two adjacent –OH groups). Identify…
Answer this question and get it marked →May–June 2024, Paper 42
(i) Give the systematic name of P (a benzene ring bearing a -COOH group and a -NO2 group at the adjacent (2-) position). (ii) P can be synthesised as shown in Fig. 7.2 by…
Answer this question and get it marked →October–November 2024, Paper 11
Ethene reacts with steam in the presence of sulfuric acid. C₂H₄ + H₂O → CH₃CH₂OH Which type of reaction is this? A acid–base B addition C hydrolysis D substitution
Answer this question and get it marked →Vitamin A contains retinol. The structure of retinol is shown: it has a substituted cyclohexene ring joined to a long unsaturated carbon chain bearing several C=C double bonds and…
Answer this question and get it marked →The structure of limonene is shown. Limonene, C₁₀H₁₆, has a cyclohexene ring with a methyl substituent and an isopropenyl (prop-1-en-2-yl) side group. What are the number of moles…
Answer this question and get it marked →The reaction of chlorine with methane is carried out in the presence of light. What is the function of the light? A to break the C–H bonds in methane B to break the chlorine…
Answer this question and get it marked →October–November 2024, Paper 12
The diagram shows the structural formula of a hydrocarbon molecule Q. Molecule Q has a six-carbon main chain that contains a C=C double bond and a C≡C triple bond. One of the…
Answer this question and get it marked →October–November 2024, Paper 13
Ethene reacts with steam in the presence of sulfuric acid. C₂H₄ + H₂O → CH₃CH₂OH Which type of reaction is this? A acid–base B addition C hydrolysis D substitution
Answer this question and get it marked →Vitamin A contains retinol. The structure of retinol is shown: it has a substituted cyclohexene ring joined to a long unsaturated carbon chain bearing several C=C double bonds and…
Answer this question and get it marked →The structure of limonene is shown. Limonene, C₁₀H₁₆, has a cyclohexene ring with a methyl substituent and an isopropenyl (prop-1-en-2-yl) side group. What are the number of moles…
Answer this question and get it marked →The reaction of chlorine with methane is carried out in the presence of light. What is the function of the light? A to break the C–H bonds in methane B to break the chlorine…
Answer this question and get it marked →October–November 2024, Paper 22
Bromoalkanes are used widely in industry, although there is increasing concern about their environmental impact. Complete Fig. 4.2 to show the mechanism for the formation of…
Answer this question and get it marked →October–November 2024, Paper 41
Benzene, C6H6, reacts with chloroethane, C2H5Cl, in the presence of a suitable catalyst to form ethylbenzene, C6H5C2H5. In the presence of the catalyst, the ion C2H5 + is formed.…
Answer this question and get it marked →October–November 2024, Paper 42
Benzene reacts with chlorine gas to form chlorobenzene. This reaction can be described as the reaction between benzene molecules and Cl+ ions. The Cl+ ions are formed by adding a…
Answer this question and get it marked →October–November 2024, Paper 43
Benzene, C6H6, reacts with chloroethane, C2H5Cl, in the presence of a suitable catalyst to form ethylbenzene, C6H5C2H5. In the presence of the catalyst, the ion C2H5 + is formed.…
Answer this question and get it marked →February–March 2023, Paper 12
Cyclohexene, C6H10, is a hydrocarbon with a six-membered ring of carbon atoms. It has several structural isomers that are straight-chain alkenes. The number of double bonds in…
Answer this question and get it marked →Exhaust gases from an internal combustion engine are made less harmful by passing them through a catalytic converter. A number of reactions take place in the catalytic converter.…
Answer this question and get it marked →Cyclohexa-1,4-diene is treated with a solution of bromine in tetrachloromethane in the dark. Cyclohexa-1,4-diene is a six-membered carbon ring with two C=C double bonds, one…
Answer this question and get it marked →2-methylbut-2-ene is reacted with hot, concentrated, acidified potassium manganate(VII) solution. What are the products of this reaction? A ethanal and propanone B ethanoic acid…
Answer this question and get it marked →February–March 2023, Paper 22
Alkenes undergo an addition reaction with a 1:1 mixture of CO and H2 to form aldehydes. Fig. 3.1 shows the reaction of propene with a 1:1 mixture of CO and H2: propene reacts to…
Answer this question and get it marked →February–March 2023, Paper 42
Tulobuterol is used in some medicines and contains a benzene ring in its structure. Describe and explain the shape of benzene. In your answer include the bond angle between carbon…
Answer this question and get it marked →May–June 2023, Paper 11
Which equation represents a reaction that proceeds through initiation, propagation and termination steps? A C4H10 + Cl2 → C4H9Cl + HCl B C5H11Br + NaOH → C5H11OH + NaBr C C6H12 +…
Answer this question and get it marked →Structural isomerism and stereoisomerism should be considered when answering this question. A set of isomeric hydrocarbons: all contain 14.3% by mass of hydrogen; all react with…
Answer this question and get it marked →May–June 2023, Paper 12
Ethane reacts with an excess of chlorine in the presence of ultraviolet light to form a mixture of products. How many of these products contain two carbon atoms and one or more…
Answer this question and get it marked →Alkynes are hydrocarbons that contain one triple C-C bond. Like alkenes, alkynes take part in addition reactions. A saturated compound can be formed. For example, ethyne, H-C-C-H,…
Answer this question and get it marked →Bromine reacts with alkenes by an electrophilic addition mechanism in which a cation is formed as an intermediate. Which mixture will produce the most stable intermediate cation?…
Answer this question and get it marked →May–June 2023, Paper 13
A mixture of ethane and an excess of chlorine is exposed to UV light. How many different products, each containing only two carbon atoms and at least one chlorine atom per…
Answer this question and get it marked →When 1-methylcyclohexene reacts with Br2 the product is X. When 1-methylcyclohexene reacts with HBr the major product is Y. Which statement is correct? A X is a mixture of two…
Answer this question and get it marked →Which two-step process converts cyclohexanol into cyclohexane-1,2-diol? Cyclohexanol (a cyclohexane ring bearing one -OH group) is converted to cyclohexane-1,2-diol (a cyclohexane…
Answer this question and get it marked →May–June 2023, Paper 21
Molecule M is present in petrol, a fuel used in cars. M is a saturated, non-cyclic hydrocarbon. M contains eight carbon atoms. Construct an equation for the complete combustion of…
Answer this question and get it marked →May–June 2023, Paper 41
State the hybridisation of the carbon atoms and the C–C–H bond angle in benzene, C₆H₆. Explain how orbital overlap leads to the formation of σ and π bonds in benzene.
Answer this question and get it marked →May–June 2023, Paper 42
Methylbenzene can undergo different reactions, as shown in Fig. 5.1: reaction 1 with H₂/Pt; reaction 2 with Br₂/UV light; reaction 3 with Br₂/FeBr₃ (giving two products). Draw…
Answer this question and get it marked →May–June 2023, Paper 43
State the hybridisation of the carbon atoms and the C-C-H bond angle in benzene, C6H6. Explain how orbital overlap leads to the formation of sigma and pi bonds in benzene.
Answer this question and get it marked →October–November 2023, Paper 11
The hydrocarbon C17H36 can be cracked. Which compound is the least likely to be produced in this reaction? A: C3H8. B: C4H8. C: C8H16. D: C16H34.
Answer this question and get it marked →Which compound has an Mr of 84 and will react with HBr to give a product with an Mr of 164.9? A: cyclohexane. B: a hexene (CH3CH2CH=CHCH2CH3, hex-3-ene). C: pentan-3-one. D: a…
Answer this question and get it marked →Beta-carotene is responsible for the orange colour of carrots; its skeletal structure is shown. Beta-carotene is oxidised by hot, concentrated, acidified KMnO4. When an individual…
Answer this question and get it marked →October–November 2023, Paper 12
The structure of compound X is shown - a chain with two C=C double bonds, one of which is a 2-methylbut-2-ene-type internal double bond and the other a terminal double bond. One…
Answer this question and get it marked →Which list contains a compound that is not made during the free radical substitution of methane with chlorine? A: CH3Cl, CCl4, C2H6. B: Cl2, CH2Cl2, CCl4. C: CH3Cl, CH2Cl2, CHCl3.…
Answer this question and get it marked →October–November 2023, Paper 13
The hydrocarbon C17H36 can be cracked. Which compound is the least likely to be produced in this reaction? A C3H8 B C4H8 C C8H16 D C16H34
Answer this question and get it marked →Which compound has an Mr of 84 and will react with HBr to give a product with an Mr of 164.9? A cyclohexane (a six-membered carbon ring). B an open-chain alkene, hept-3-ene drawn…
Answer this question and get it marked →beta-carotene is responsible for the orange colour of carrots. [The skeletal structure of beta-carotene is shown: a long conjugated polyene chain bearing several CH3 substituents,…
Answer this question and get it marked →October–November 2023, Paper 21
Compounds C and D are alkenes with the same molecular formula, C5H10. [Fig. 4.1: C is 2-methylbut-2-ene, (CH3)2C=CHCH3, drawn skeletally. D is 3-methylbut-1-ene, (CH3)2CHCH=CH2,…
Answer this question and get it marked →October–November 2023, Paper 23
Compounds C and D are alkenes with the same molecular formula, C5H10. [Fig. 4.1: C is 2-methylbut-2-ene, (CH3)2C=CHCH3, drawn skeletally. D is 3-methylbut-1-ene, (CH3)2CHCH=CH2,…
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