CAIE A-Level Chemistry 14.1.2 Combustion and Substitution of Alkanes

Practise alkane combustion equations and free-radical substitution with chlorine or bromine under ultraviolet light.

Exam points

balance complete combustion to CO2 and H2O and incomplete combustion to CO and/or carbon where specified
state Cl2 or Br2 and ultraviolet light for substitution of a C–H hydrogen by halogen
recognise further substitution and product mixtures rather than assuming a single monohalogenated product

[Maximum number: 2]

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

[ 2 ]

(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)

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

[ 1 ]

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14.1.2—Describe question 1

Question (a)

Question (i)

Question (ii)