Alkanes as fuels and pollutionEdexcel A-Level Chemistry: Subtopic test

1. 1
   A refinery separates crude oil by fractional distillation. One fraction contains mainly heptane, C₇H₁₆, a straight-chain alkane. Part of this fraction is processed further so that it can be blended into petrol for use in car engines.

   (a)

   Which statement correctly describes heptane?

   [1 mark]

   • AIt is an unsaturated hydrocarbon with general formula CₙH₂ₙ
   • BIt is a saturated hydrocarbon with general formula CₙH₂ₙ₊₂
   • CIt is a saturated hydrocarbon with general formula CₙH₂ₙ
   • DIt is an unsaturated hydrocarbon with general formula CₙH₂ₙ₊₂

   (b)

   Which of these could be a product of reforming heptane?

   [1 mark]

   • A2,2,3-trimethylbutane
   • BHeptan-1-ol
   • CCarbon dioxide and water
   • DPropane and butane

   (c)

   Explain why the refinery reforms some of the straight-chain alkanes in this fraction before blending them into petrol.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A petrol car is driven on a motorway. Air enters the engine and the fuel burns at a very high temperature in a limited supply of oxygen, so the exhaust gases contain carbon monoxide, nitrogen monoxide, unburned hydrocarbons and carbon particulates before they pass through the exhaust system.

   (a)

   Which pollutant forms when nitrogen and oxygen from the air react at the high temperature inside the engine?

   [1 mark]

   • ACarbon monoxide
   • BUnburned hydrocarbons
   • CNitrogen monoxide
   • DCarbon particulates

   (b)

   Why is carbon monoxide in the exhaust gases a danger to people?

   [1 mark]

   • AIt dissolves in rain water to form an acidic solution that irritates the lungs
   • BIt reacts with oxygen in the lungs to form carbon dioxide, which is poisonous
   • CIt forms solid soot deposits on the lining of the lungs
   • DIt binds strongly to haemoglobin in blood, so less oxygen can be carried around the body

   (c)

   Write an equation for the formation of nitrogen monoxide in the engine and explain why it forms in the engine but not in the cold air outside the car.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The exhaust system of the car contains a catalytic converter. This is a honeycomb of ceramic coated with a thin layer of platinum, palladium and rhodium. The exhaust gases pass through it before leaving the car.

   (a)

   The converter helps to solve two pollution problems when carbon monoxide reacts with nitrogen monoxide. Write an equation for this reaction and explain how it reduces each problem.

   [3 marks]

   (b)

   In a test, a car produces 2.40 g of carbon monoxide in one minute, and all of it reacts in the converter with nitrogen monoxide: 2CO + 2NO → 2CO₂ + N₂. Calculate the mass of carbon dioxide formed and the volume of nitrogen formed at room temperature and pressure, in one minute. (Ar: C = 12.0, O = 16.0; 1 mol of gas occupies 24.0 dm³ at room temperature and pressure.)

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A country wants to reduce its use of fossil fuels for transport. Its vehicles currently run on petrol and diesel made from crude oil. The government is considering blending ethanol (made by fermenting plant sugars) into petrol and using biodiesel (made from plant oils such as rapeseed oil).

   (a)

   Evaluate the use of biodiesel and ethanol from plants, compared with petrol and diesel from crude oil, as fuels for the country's transport.

   [6 marks]

   (b)

   The country's refinery separates crude oil by fractional distillation but finds that there is too little petrol and too much of a fraction containing long-chain alkanes. Explain how fractional distillation separates crude oil and how cracking helps the refinery to meet the demand for petrol. Include an equation for the cracking of dodecane, C₁₂H₂₆, to form one alkane with eight carbon atoms and one other product.

   [6 marks]

   Total for question 4: 12 marks

End of questions