AQA GCSE Chemistry (8462), Higher tier · Organic chemistry › Reactions of alkenes and alcohols
Practise Reactions of alkenes. 15 exam-style questions 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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Ethene reacts with hydrogen. Name the product.
Ethane
Ethene reacts with steam to produce ethanol. What else is needed for this reaction?
A catalyst.
Write a balanced equation for the complete combustion of ethene.
C2H4 + 3O2 → 2CO2 + 2H2O
Name the alkene.
Pentene
An alkene, X, reacts in these ways:
with hydrogen it forms butane
with steam it forms butanol
with chlorine it forms a compound with the formula C4H8Cl2.
Name alkene X.
Butene
Bromine water is added to an alkene and shaken. Give the colour change you would see.
Orange to colourless
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) Ethene reacts with hydrogen. Name the product.[1]
(b) What is needed for an alkene to react with hydrogen?[1]
(c) What type of reaction happens when bromine reacts with ethene? Tick (✓) one box.[1]
Addition
Displacement
Neutralisation
Thermal decomposition
(d) Alkenes usually burn in air with a smoky flame. Give the reason for this.[1]
Show the answer and mark scheme
(a)Answer: Ethane
ethane
(b)Answer: A catalyst (nickel).
a catalyst (nickel)
(c)Answer: Addition
(d)Answer: Incomplete combustion.
incomplete combustion
Question 2Medium7 marks
Ethene, C2H4, is the simplest alkene.
(a) Write a balanced equation for the complete combustion of ethene.[2]
(b) Alkenes often burn in air with a smoky flame. Explain why, and name one product of incomplete combustion.[2]
(c) Write a balanced equation for the reaction of ethene with steam.[1]
(d) Give two conditions used for the reaction of ethene with steam.[2]
Show the answer and mark scheme
(a)Answer: C2H4 + 3O2 → 2CO2 + 2H2O
correct formulae: C2H4 + O2 → CO2 + H2O
balanced: C2H4 + 3O2 → 2CO2 + 2H2O
(b)Answer: There is not enough oxygen for complete combustion; carbon (soot) forms.
incomplete combustion (not enough oxygen for all of the carbon to be oxidised)
carbon (soot) / carbon monoxide
(c)Answer: C2H4 + H2O → C2H5OH
C2H4 + H2O → C2H5OH
(d)Answer: A catalyst (phosphoric acid) and a high temperature (about 300 °C).
a catalyst (e.g. phosphoric acid)
a high temperature (about 300 °C)
a high pressure (about 60 to 70 atmospheres)
Question 3Hard7 marks
(a) Explain why bromine water is decolourised by alkenes but not by alkanes.[2]
(b) A student found that 0.70 g of an alkene reacted with exactly 1.60 g of bromine, Br2. One mole of the alkene reacts with one mole of bromine. Determine the relative formula mass (Mr) and the molecular formula of the alkene. Relative atomic masses (Ar): H = 1 C = 12 Br = 80[4]
(c) Name the alkene.[1]
Show the answer and mark scheme
(a)Answer: Alkenes have a C=C double bond, so bromine adds across it to form a colourless product; alkanes have no double bond.
alkenes have a C=C double bond, so bromine adds across it (addition reaction) forming a colourless product
alkanes have no C=C double bond / are saturated, so no addition reaction happens