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Cambridge International AS Level Chemistry

Topic 14
Hydrocarbons

Topic 14 covers the alkanes and the alkenes: how alkanes are obtained and why they are unreactive, free-radical substitution, and then the production, electrophilic addition reactions, oxidation and polymerisation of alkenes.

Alkene bonding and geometrical isomerism sit in Topic 13 and polymers in Topic 20, and are linked from these pages.

Exam Papers
Papers 1 & 2
9701/1 and 9701/2 (AS Level)
Learning Outcomes
14.1.1 – 14.2.5
11 outcomes with sub-points
Sub-topics
2 lessons
Alkanes and Alkenes
Exam Board
Cambridge
CIE 9701 (2025-2027)

Revision Notes

2 revision notes, in the order the specification teaches them.

A tetrahedral alkane molecule and a gas flame
1

Alkanes

Production of alkanes, combustion, free-radical substitution and its mechanism, cracking, and the environmental consequences of burning alkanes.

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A carbon to carbon double bond
2

Alkenes

Producing alkenes, electrophilic addition, addition reactions with hydrogen, halogens, hydrogen halides, steam and KMnO4, and addition polymerisation.

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MCQ Bank

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Written, drawn and worked exam practice on this topic.

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Revision Game

Match reagents to products, with your board's reagents and conditions.

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Study Cards

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Specification

Every specification point in this topic, in the exam board's own words. Rate how confident you are with each one.

Official Cambridge documentsSyllabus (opens the Cambridge website in a new tab)

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14.1.1

  1. a

    recall the reaction (reagents and conditions) by which alkanes can be produced: addition of hydrogen to an alkene in a hydrogenation reaction, H2(g) and Pt/Ni catalyst and heat

    Revise
  2. b

    recall the reaction (reagents and conditions) by which alkanes can be produced: cracking of a longer chain alkane, heat with Al2O3

    Revise

14.1.2

  1. a i

    describe the complete combustion of alkanes

    Revise
  2. a ii

    describe the incomplete combustion of alkanes

    Revise
  3. b i

    describe the free-radical substitution of alkanes by Cl2 in the presence of ultraviolet light, as exemplified by the reactions of ethane

    Revise
  4. b ii

    describe the free-radical substitution of alkanes by Br2 in the presence of ultraviolet light, as exemplified by the reactions of ethane

    Revise

14.1.3

  1. a

    describe the mechanism of free-radical substitution with reference to the initiation step

    Revise
  2. b

    describe the mechanism of free-radical substitution with reference to the propagation steps

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  3. c

    describe the mechanism of free-radical substitution with reference to the termination steps

    Revise

14.1.4

  1. 14.1.4

    suggest how cracking can be used to obtain more useful alkanes and alkenes of lower Mr from heavier crude oil fractions

    Revise

14.1.5

  1. a

    understand the general unreactivity of alkanes, including towards polar reagents, in terms of the strength of the C–H bonds

    Revise
  2. b

    understand the general unreactivity of alkanes, including towards polar reagents, in terms of the relative lack of polarity of the C–H bonds

    Revise

14.1.6

  1. a

    recognise the environmental consequences of carbon monoxide arising from the combustion of alkanes in the internal combustion engine

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  2. b

    recognise the environmental consequences of oxides of nitrogen arising from the combustion of alkanes in the internal combustion engine

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  3. c

    recognise the environmental consequences of unburnt hydrocarbons arising from the combustion of alkanes in the internal combustion engine

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  4. d

    recognise the catalytic removal of carbon monoxide, oxides of nitrogen and unburnt hydrocarbons arising from the combustion of alkanes in the internal combustion engine

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14.2.1

  1. a

    recall the reaction (including reagents and conditions) by which alkenes can be produced: elimination of HX from a halogenoalkane by ethanolic NaOH and heat

    Revise
  2. b i

    recall the reaction (including reagents and conditions) by which alkenes can be produced: dehydration of an alcohol, by using a heated catalyst (e.g. Al2O3)

    Revise
  3. b ii

    recall the reaction (including reagents and conditions) by which alkenes can be produced: dehydration of an alcohol, by using a concentrated acid (e.g. concentrated H2SO4)

    Revise
  4. c

    recall the reaction (including reagents and conditions) by which alkenes can be produced: cracking of a longer chain alkane

    Revise

14.2.2

  1. a (i)

    describe the electrophilic addition of hydrogen to alkenes in a hydrogenation reaction, H2(g) and Pt/Ni catalyst and heat

    Revise
  2. a (ii)

    describe the electrophilic addition of steam to alkenes, H2O(g) and H3PO4 catalyst

    Revise
  3. a (iii)

    describe the electrophilic addition of a hydrogen halide, HX(g), to alkenes at room temperature

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  4. a (iv)

    describe the electrophilic addition of a halogen, X2, to alkenes

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  5. b

    describe the oxidation of alkenes by cold dilute acidified KMnO4 to form the diol

    Revise
  6. c i

    describe the oxidation of alkenes by hot concentrated acidified KMnO4 leading to the rupture of the carbon–carbon double bond

    Revise
  7. c ii

    use the identities of the products of oxidation by hot concentrated acidified KMnO4 to determine the position of alkene linkages in larger molecules

    Revise
  8. d i

    describe addition polymerisation exemplified by the reactions of ethene

    Revise
  9. d ii

    describe addition polymerisation exemplified by the reactions of propene

    Revise

14.2.3

  1. 14.2.3

    describe the use of aqueous bromine to show the presence of a C=C bond

    Revise

14.2.4

  1. a

    describe the mechanism of electrophilic addition in alkenes, using bromine/ethene as an example

    Revise
  2. b

    describe the mechanism of electrophilic addition in alkenes, using hydrogen bromide/propene as an example

    Revise

14.2.5

  1. a

    describe and explain the inductive effects of alkyl groups on the stability of primary, secondary and tertiary cations formed during electrophilic addition

    Revise
  2. b

    use the inductive effects of alkyl groups on the stability of primary, secondary and tertiary cations to explain Markovnikov addition

    Revise