CAIE A-Level Chemistry 14.1 Alkanes Question Bank

Practise alkane reactions through combustion equations, cracking products, radical substitution steps, unreactivity explanations and exhaust pollutant removal.

Exam points

write balanced alkane combustion equations and link products to oxygen supply
complete initiation, propagation and termination equations for halogen substitution
use cracking and catalytic converter evidence to select products, catalysts and pollutants

Covered syllabus points

14.1.1—Preparation of alkanes 14.1.2—Describe 14.1.3—Mechanism: free-radical substitution 14.1.4—Suggest how cracking can be used to obtain 14.1.5—The general unreactivity of alkanes 14.1.6—Combustion pollutants and catalysts

[Maximum number: 1]

Different hydrocarbon mixtures produced from fractional distillation of crude oil have different uses.

State the compound that is heated with long-chain hydrocarbons to produce more useful smaller alkanes and alkenes.

$\mathrm{Al}_{2} \mathrm{O}_{3}$ / aluminium oxide

[Maximum number: 3]

Allyl chloride is an important chemical used in the manufacture of plastics, pharmaceuticals and pesticides.

allyl chloride

(a)

Allyl chloride can be produced by many different methods. The most common method is chlorination of propene which proceeds via a free-radical substitution mechanism.

Figure for Question (a) — CAIE A-Level Chemistry AS

[ 3 ]

(i)

The initiation step in this reaction is the formation of chlorine radicals ( $\mathrm{C} l^{\bullet}$ ) from $\mathrm{Cl}_{2}$ molecules.

State the conditions required to initiate this reaction.

[ 1 ]

(ii)

The propenyl radical, $\mathrm{CH}_{2}=\mathrm{CHCH}_{2}$ , is formed in the first propagation step of the reaction. Write an equation to show the formation of $\mathrm{CH}_{2}=\mathrm{CHCH}_{2}{ }^{\bullet}$ in this propagation step.

[ 1 ]

$\begin{aligned} \mathrm{CH}_{2}=\mathrm{CHCH}_{3}+\mathrm{C} l^{\bullet} \rightarrow \mathrm{CH}_{2}=\mathrm{CHCH}_{2}^{\bullet}+\mathrm{HCl} \mathrm{OR} \mathrm{C}_{3} \mathrm{H}_{6}+\mathrm{C} l^{\bullet} \rightarrow \rightarrow \mathrm{C}_{3} \mathrm{H}_{5}{ }^{\bullet}+\mathrm{HCl} \end{aligned}$

(iii)

Explain why the free-radical substitution reaction gives a low yield of allyl chloride.

[ 1 ]

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Covered syllabus points

14.1 Alkanes question 1

14.1 Alkanes question 2

Question (a)

Question (i)

Question (ii)

Question (iii)