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CAIE IGCSE Chemistry 11.5 Alkenes Questions

Practise alkene reactions and tests by using C=C bonding, cracking equations, bromine water and addition-product reasoning.

Syllabus
2026–2028
Course
Chemistry 0620

Exam points

  • use C=C and bromine water decolourisation to recognise unsaturated compounds
  • complete cracking equations that form alkenes, hydrogen or smaller alkanes
  • explain addition reactions from a single product and a reacting carbon-carbon double bond

Covered syllabus points

11.5.1—Bonding in alkenes includes a double11.5.2—Manufacture of alkenes and hydrogen by11.5.3—Reasons for the cracking of larger11.5.4—Test to distinguish between saturated11.5.5—In an addition reaction only one11.5.6—Alkene addition reactions with

Question 1

[Maximum number: 1]

38 P, Q, R and S are four organic compounds.
P is an unsaturated hydrocarbon.
Q burns but otherwise is unreactive.
R contains a C-C single bond and a C=C double bond.
S undergoes addition polymerisation.
Which compounds are alkenes?

A

P and R only

B

P, R and S

C

P, Q and S

D

Q, R and S

Question 2

[Maximum number: 1]

Many organic compounds contain carbon and hydrogen only.

Propene, C3H6\mathrm{C}_{3} \mathrm{H}_{6}, can be produced by heating C11H24\mathrm{C}_{11} \mathrm{H}_{24}. The products of the reaction are propene, hydrogen and one other product in a 1: 1: 1 mole ratio.

Complete the symbol equation for this reaction.

C11H24→C3H6+H2+\mathrm{C}_{11} \mathrm{H}_{24} \rightarrow \mathrm{C}_{3} \mathrm{H}_{6}+\mathrm{H}_{2}+

Question 3

[Maximum number: 1]

Which compound rapidly decolourises aqueous bromine?

A

propane

B

propanoic acid

C

propanol

D

propene

Question 4

[Maximum number: 1]

Ethanol is made by reacting ethene with steam in an industrial process.

Explain why this reaction is an addition reaction.

Question 5

[Maximum number: 1]

Alkenes react with steam in an addition reaction.

Some alkenes produce only one alcohol product.
Some alkenes produce two different alcohols which are structural isomers.
Which row gives the number of alcohol isomers formed when ethene reacts with steam and when propene reacts with steam?

number of alcohol isomers formed
ethene + steam

number of alcohol isomers formed
propene + steam

1

1

1

2

2

1

2

2

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