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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
Topic Parts
2 parts
Alkanes and Alkenes
Exam Board
Cambridge
CIE 9701 (2025-2027)

Revision Notes

Work through each part of Cambridge Topic 14 in a structured sequence.

Saturated
Alkanes
1

Alkanes

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

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Unsaturated
Alkenes
2

Alkenes

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

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Specification Coverage

Topic 14 Hydrocarbons – Cambridge International AS Level Chemistry

The following Cambridge learning outcomes state what candidates should be able to do for Topic 14. Wording is taken from the Cambridge International AS & A Level Chemistry 9701 syllabus for 2025 to 2027.

14.1 Alkanes

14.1.1
recall the reactions (reagents and conditions) by which alkanes can be produced:
(a)
addition of hydrogen to an alkene in a hydrogenation reaction, H2(g) and Pt/Ni catalyst and heat
(b)
cracking of a longer chain alkane, heat with Al2O3
14.1.2
describe:
(a)
the complete and incomplete combustion of alkanes
(b)
the free-radical substitution of alkanes by Cl2 or Br2 in the presence of ultraviolet light, as exemplified by the reactions of ethane
14.1.3
describe the mechanism of free-radical substitution with reference to the initiation, propagation and termination steps
14.1.4
suggest how cracking can be used to obtain more useful alkanes and alkenes of lower Mr from heavier crude oil fractions
14.1.5
understand the general unreactivity of alkanes, including towards polar reagents in terms of the strength of the C–H bonds and their relative lack of polarity
14.1.6
recognise the environmental consequences of carbon monoxide, oxides of nitrogen and unburnt hydrocarbons arising from the combustion of alkanes in the internal combustion engine and of their catalytic removal

14.2 Alkenes

14.2.1
recall the reactions (including reagents and conditions) by which alkenes can be produced:
(a)
elimination of HX from a halogenoalkane by ethanolic NaOH and heat
(b)
dehydration of an alcohol, by using a heated catalyst (e.g. Al2O3) or a concentrated acid (e.g. concentrated H2SO4)
(c)
cracking of a longer chain alkane
14.2.2
describe the following reactions of alkenes:
(a)
the electrophilic addition of (i) hydrogen in a hydrogenation reaction, H2(g) and Pt/Ni catalyst and heat; (ii) steam, H2O(g) and H3PO4 catalyst; (iii) a hydrogen halide, HX(g), at room temperature; (iv) a halogen, X2
(b)
the oxidation by cold dilute acidified KMnO4 to form the diol
(c)
the oxidation by hot concentrated acidified KMnO4 leading to the rupture of the carbon–carbon double bond and the identities of the subsequent products to determine the position of alkene linkages in larger molecules
(d)
addition polymerisation exemplified by the reactions of ethene and propene
14.2.3
describe the use of aqueous bromine to show the presence of a C=C bond
14.2.4
describe the mechanism of electrophilic addition in alkenes, using bromine/ethene and hydrogen bromide/propene as examples
14.2.5
describe and explain the inductive effects of alkyl groups on the stability of primary, secondary and tertiary cations formed during electrophilic addition (this should be used to explain Markovnikov addition)