Ethanol burns in air
4 marks · NormalEthanol is a member of the alcohol homologous series. When ethanol is burned in air, it reacts with oxygen.
Write a balanced chemical equation for the complete combustion of ethanol.
Give one use of ethanol as a fuel and explain why it is considered a biofuel.
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(a) \ce{C2H5OH(l) + 3O2(g) -> 2CO2(g) + 3H2O(l)} · must show Correct formulae for ethanol, oxygen, carbon dioxide, water; correct balancing
(b) Ethanol can be used as a fuel for cars (or as a petrol additive). It is a biofuel because it is produced from renewable biological sources such as sugar cane or corn. · must show Identifies ethanol as a fuel/additive, Explains biofuel (produced from plants/renewable sources)
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Marking points
M1 (a) · 1 mark · Writes correct reactants and products (ethanol, oxygen, carbon dioxide, water).
A1 (a) · 1 mark · Balances equation correctly: \ce{C2H5OH(l) + 3O2(g) -> 2CO2(g) + 3H2O(l)}
B1 (b) · 1 mark · States use of ethanol as a fuel or as an additive to petrol.
B2 (b) · 1 mark · Explains that ethanol is considered a biofuel as it is made from renewable/bio sources.
Worked solution
a) The balanced chemical equation for the complete combustion of ethanol is:
b) Ethanol can be used in car engines, either as a fuel on its own or as an additive to petrol. Ethanol is considered a biofuel because it is produced from biological materials like sugar cane, making it renewable.