Crude Oil
6 marks · NormalCombustion reactions of hydrocarbons from different fractions have important uses.
State two products formed when a hydrocarbon fuel undergoes complete combustion.
Write a word or symbol equation for the complete combustion of methane.
Explain why carbon monoxide is formed during incomplete combustion of hydrocarbons and why it is dangerous.
Gasoline is commonly used as a fuel in cars. Explain why gasoline is suitable for this use.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Carbon dioxide and water · must show carbon dioxide, water
(b) CH4 + 2O2 -> CO2 + 2H2O or 'methane + oxygen -> carbon dioxide + water' · must show correct balanced symbol or word equation
(c) Incomplete combustion occurs when there is not enough oxygen. Carbon monoxide is dangerous because it is poisonous and prevents blood from carrying oxygen. · must show not enough oxygen, carbon monoxide prevents oxygen transport in blood/is poisonous
(d) Gasoline is suitable because it is a liquid fuel with a high energy content and its hydrocarbons burn easily in car engines. · must show high energy content, burns easily/efficiently in engines
Common mistakes: Confusing products of combustion; Incorrect or unbalanced equation; Omitting explanation of why carbon monoxide is dangerous; Not linking properties of gasoline to its use
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Names both carbon dioxide and water as products of complete combustion.
B2 (b) · 1 mark · Writes correct word or balanced symbol equation for combustion of methane.
M1 (c) · 1 mark · Explains that incomplete combustion is caused by insufficient oxygen.
B3 (c) · 1 mark · Explains why carbon monoxide is dangerous to humans.
M2 (d) · 1 mark · Identifies that gasoline has a high energy content/efficient burning.
B4 (d) · 1 mark · States that gasoline burns well/easily in car engines or is a suitable liquid fuel.
Worked solution
a) The products are carbon dioxide and water.
b) Symbol equation: CH4 + 2O2 -> CO2 + 2H2O
c) Incomplete combustion occurs when there is not enough oxygen; this produces carbon monoxide, which is a poisonous gas. Carbon monoxide prevents haemoglobin from carrying oxygen in the blood.
d) Gasoline is a liquid that contains hydrocarbons with a high energy content, making it suitable as a car fuel. It evaporates and burns easily in car engines.