AQA GCSE Chemistry (8462), Higher tier · Organic chemistry › Reactions of alkenes and alcohols
Practise Structure and formulae of alkenes. 11 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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What is the general formula of the alkenes?
CnH2n
Draw the displayed formula of propene.
Three carbon atoms in a chain with one C=C double bond and six hydrogen atoms.
Name the functional group that all alkenes contain.
Carbon–carbon double bond (C=C)
In a molecule of cyclohexane, six carbon atoms are joined in a ring by single bonds. Each carbon atom is also bonded to two hydrogen atoms. Give the molecular formula of cyclohexane.
C6H12
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
(a) What is the general formula of the alkenes?[1]
(b) Name the alkene with the formula C3H6.[1]
(c) Alkenes are described as unsaturated. What does this mean?[1]
(d) Draw the displayed formula of ethene, C2H4.[1]
Show the answer and mark scheme
(a)Answer: CnH2n
CnH2n
(b)Answer: Propene
propene
(c)Answer: They contain a carbon–carbon double bond.
they contain a carbon–carbon double bond (C=C) / they have two fewer hydrogen atoms than the alkane with the same number of carbon atoms
(d)Answer: Two carbon atoms joined by a double bond, each bonded to two hydrogen atoms.
two C atoms joined by a double bond, each bonded to two H atoms
Question 2Medium3 marks
A technician has two colourless liquids, one an alkane and one an alkene, but does not know which is which.
Describe a chemical test the technician could use to identify which liquid is the alkene, including the result expected.[3]
Show the answer and mark scheme
Answer: Add a few drops of each liquid to separate samples of bromine water and shake. The liquid that turns the bromine water from orange to colourless is the alkene; the alkane causes no colour change.
add a few drops of each liquid to separate samples of bromine water (and shake/mix)
the alkene turns the bromine water from orange to colourless
the alkane causes no colour change (the bromine water stays orange)
Question 3Hard5 marks
In a molecule of cyclohexane, six carbon atoms are joined in a ring by single bonds. Each carbon atom is also bonded to two hydrogen atoms.
(a) Give the molecular formula of cyclohexane.[1]
(b) A student says: 'Any hydrocarbon with the general formula CnH2n must be an alkene.' Use cyclohexane to evaluate this statement.[2]
(c) Predict what you would see if cyclohexane were shaken with bromine water. Give a reason for your answer.[2]
Show the answer and mark scheme
(a)Answer: C6H12
C6H12
(b)Answer: The statement is wrong: cyclohexane (C6H12) fits CnH2n (n = 6), but it has only single bonds and no C=C double bond, so it is not an alkene.
cyclohexane fits the general formula CnH2n (n = 6)
but it has no C=C double bond (only single bonds), so it is not an alkene: the statement is wrong
(c)Answer: The bromine water would stay orange, because cyclohexane is saturated (it has no C=C double bond).