Combustion of alkanes and pollutionAQA A-Level Chemistry: Subtopic test

1. 1
   A petrol engine burns octane, C₈H₁₈, in a limited supply of air. A mechanic notices that the exhaust gas contains carbon monoxide and black particles.

   (a)

   Which equation represents the incomplete combustion of octane to form carbon monoxide?

   [1 mark]

   • AC₈H₁₈ + 12½O₂ → 8CO₂ + 9H₂O
   • BC₈H₁₈ + 8½O₂ → 8CO₂ + 9H₂O
   • CC₈H₁₈ + 12½O₂ → 8CO + 9H₂O
   • DC₈H₁₈ + 8½O₂ → 8CO + 9H₂O

   (b)

   What are the black particles in the exhaust gas?

   [1 mark]

   • ASulfur dioxide
   • BCarbon
   • CNitrogen oxides
   • DWater droplets

   (c)

   Explain why the exhaust gas contains carbon monoxide and carbon when the supply of air is limited.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A modern petrol car has a catalytic converter containing platinum and rhodium on a ceramic honeycomb. The exhaust gases leaving the engine contain nitrogen oxides (NOx), carbon monoxide and unburned hydrocarbons.

   (a)

   How are the nitrogen oxides in the exhaust gases formed?

   [1 mark]

   • ANitrogen and oxygen from the air react at the high temperatures in the engine
   • BPetrol contains nitrogen compounds that react with water
   • CNitrogen is produced by the incomplete combustion of petrol
   • DThe catalytic converter reacts nitrogen with carbon dioxide

   (b)

   Which equation represents a reaction that takes place in the catalytic converter?

   [1 mark]

   • ANO + CO → N₂ + CO₂
   • B2NO₂ + 2CO → N₂ + 2CO₂
   • C2NO + 2CO → N₂ + 2CO₂
   • D2NO + CO → N₂ + CO₂

   (c)

   Hexane, C₆H₁₄, is one of the unburned hydrocarbons in the exhaust gases. Write an equation for its complete oxidation in the catalytic converter.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An oil-fired power station burns a fuel oil that contains sulfur impurities. Before the flue gases are released, they are passed through a wet mixture of calcium carbonate in water.

   (a)

   Explain why sulfur dioxide is formed when the fuel oil is burned, and describe one environmental problem that it causes.

   [3 marks]

   (b)

   Explain why calcium carbonate and calcium oxide can both be used to remove sulfur dioxide from the flue gases. Write an equation for the reaction of sulfur dioxide with each of them.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A city council is investigating air pollution. Petrol cars in the city emit carbon monoxide, nitrogen oxides, carbon particles and unburned hydrocarbons. A nearby oil-fired power station burns fuel oil containing sulfur and could fit a flue gas scrubber that uses calcium oxide.

   (a)

   Explain how each of the four pollutants emitted by the petrol cars is formed, and how a catalytic converter reduces the emission of the gaseous pollutants.

   [6 marks]

   (b)

   Evaluate whether the power station should fit a flue gas scrubber to remove sulfur dioxide, using calcium oxide or calcium carbonate.

   [6 marks]

   Total for question 4: 12 marks

End of questions