Crude oil, fuels and pollutantsEdexcel International A Level Chemistry: Subtopic test

1. 1
   A refinery heats crude oil, a mixture of hydrocarbons, and feeds the vapour into a fractionating column that is hottest at the bottom and coolest at the top. Fractions are drawn off at different heights: refinery gas, petrol (about C₅ to C₁₀), kerosene (about C₁₀ to C₁₆) and diesel (about C₁₄ to C₂₀), with a residue left at the bottom.

   (a)

   Why is diesel drawn off lower in the column than petrol?

   [1 mark]

   • ADiesel molecules contain stronger covalent bonds, which need more energy to break.
   • BDiesel molecules are longer, so they have stronger London forces and condense at a higher temperature.
   • CDiesel molecules are polar, so they form hydrogen bonds with each other.
   • DDiesel molecules have a lower relative molecular mass, so they condense more easily.

   (b)

   Which process converts long-chain alkanes from the heavy fractions into shorter alkanes and alkenes?

   [1 mark]

   • AFractional distillation
   • BReforming
   • CCombustion
   • DCracking

   (c)

   Write an equation for the cracking of dodecane, C₁₂H₂₆, to give ethene and one other hydrocarbon, and state one reason why refineries crack heavy fractions.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A garage runs a petrol car engine in a closed workshop to test it. The petrol contains traces of sulfur compounds, and the engine becomes hot enough for nitrogen from the air to react. The exhaust gas contains carbon monoxide, oxides of nitrogen, sulfur dioxide, carbon particulates and unburned hydrocarbons.

   (a)

   Which equation shows how nitrogen monoxide forms in the engine?

   [1 mark]

   • AN₂ + O₂ → 2NO, at the high temperature inside the cylinder
   • BN₂ + 3H₂ → 2NH₃, using hydrogen from the fuel
   • C2C + O₂ → 2CO, from incomplete combustion of the fuel
   • DS + O₂ → SO₂, from sulfur compounds in the fuel

   (b)

   Which pair of exhaust gases is mainly responsible for acid rain?

   [1 mark]

   • ACarbon monoxide and unburned hydrocarbons
   • BCarbon particulates and carbon monoxide
   • CSulfur dioxide and nitrogen dioxide
   • DCarbon dioxide and carbon monoxide

   (c)

   Explain why running the engine in a closed workshop is dangerous because of carbon monoxide.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician studies the combustion of octane, C₈H₁₈, in a petrol engine. Take the molar volume of a gas at room temperature and pressure to be 24.0 dm³ mol⁻¹. Relative atomic masses: H = 1.0, C = 12.0.

   (a)

   Write balanced equations for (i) the complete combustion of octane, (ii) incomplete combustion of octane to carbon monoxide and water only, (iii) incomplete combustion of octane to carbon particulates (carbon) and water only.

   [3 marks]

   (b)

   A car burns 57.0 g of octane completely. Calculate the volume of carbon dioxide produced, and explain why increasing the concentration of carbon dioxide in the atmosphere is a concern.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A government panel is reviewing how crude oil is turned into transport fuels, and whether bioethanol or hydrogen should replace petrol to cut the contribution of transport to climate change.

   (a)

   Petrol is made from crude oil by fractional distillation, cracking and reforming. Explain how each process helps to provide petrol of the quality needed, including one equation for cracking and one for reforming.

   [6 marks]

   (b)

   Evaluate whether replacing petrol with bioethanol or hydrogen would reduce the contribution of transport to climate change, with reference to carbon neutrality.

   [6 marks]

   Total for question 4: 12 marks

End of questions