As fuels
4 marks · NormalThis question is about combustion of hydrocarbons.
Write the word equation for the complete combustion of propane.
State the two main products formed during complete combustion of a hydrocarbon.
Explain, using your knowledge of incomplete combustion, why burning a hydrocarbon in a limited supply of air may produce a dangerous gas.
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(a) propane + oxygen → carbon dioxide + water · must show propane, oxygen, carbon dioxide, water
(b) carbon dioxide and water · must show carbon dioxide, water
(c) Incomplete combustion occurs when there is not enough oxygen, which can produce carbon monoxide, a poisonous gas that prevents blood from carrying oxygen. · must show carbon monoxide as dangerous gas, due to insufficient oxygen/incomplete combustion, reason why CO is dangerous
Common mistakes: naming hydrogen instead of water as a combustion product; stating carbon as the dangerous gas, not carbon monoxide
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Marking points
B1 (a) · 1 mark · Correct word equation for complete combustion of propane (propane + oxygen → carbon dioxide + water).
B2 (b) · 1 mark · Names both main products: carbon dioxide and water.
M1 (c) · 1 mark · Mentions incomplete combustion occurs or not enough oxygen is present.
A1 (c) · 1 mark · States carbon monoxide is produced and gives a valid reason for its danger (e.g., poisonous, prevents blood carrying oxygen).
Worked solution
a) The word equation: propane + oxygen → carbon dioxide + water
b) The two main products are carbon dioxide and water.
c) In incomplete combustion, there is not enough oxygen for complete reaction. This can produce carbon monoxide, which is dangerous because it is poisonous and prevents the blood from carrying oxygen.