1. 1
   A technician separates a sample of crude oil in a laboratory fractionating column. The crude oil is heated until it vaporises, and the vapours rise up the column, which is hotter at the bottom and cooler at the top. Different fractions condense at different heights and are collected separately.

   (a)

   Which statement correctly describes crude oil?

   [1 mark]

   • AA single pure hydrocarbon compound
   • BA complex mixture of hydrocarbon molecules with chains or rings of carbon atoms
   • CA mixture of only alkene molecules produced by cracking
   • DAn element found in the Earth's early atmosphere

   (b)

   The technician collects a fraction near the bottom of the column, where the temperature is highest. This fraction contains large hydrocarbon molecules with high boiling points. Which property would this fraction most likely have compared with a fraction collected near the top?

   [1 mark]

   • ALower viscosity and easier to ignite
   • BNo hydrogen atoms in its molecules
   • CThe same viscosity but a lower boiling point
   • DHigher viscosity and harder to ignite

   (c)

   The technician labels four collected fractions as gases, petrol, kerosene and bitumen. State one everyday use for kerosene and one everyday use for bitumen.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A homeowner has a gas boiler that burns methane. An engineer tests the boiler and finds that when the air supply is restricted, the flame burns with a smoky yellow colour instead of a clean blue colour, and a build-up of soot forms on the surrounding surfaces.

   (a)

   Which type of combustion is occurring when the air supply is restricted?

   [1 mark]

   • AIncomplete combustion, producing carbon and carbon monoxide
   • BComplete combustion, producing only carbon dioxide and water
   • CNeutralisation, producing a salt and water
   • DThermal decomposition, producing an oxide and carbon dioxide

   (b)

   The engineer warns the homeowner that the gas produced during incomplete combustion is particularly dangerous because it is colourless, odourless and toxic. Which gas is the engineer referring to?

   [1 mark]

   • ACarbon dioxide
   • BOxygen
   • CCarbon monoxide
   • DSulfur dioxide

   (c)

   Explain why carbon monoxide produced by the faulty boiler is dangerous to the people living in the house.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A haulage company runs a fleet of diesel lorries. Diesel fuel from a particular supplier contains small amounts of sulfur impurities. Environmental scientists have found that rainwater collected near the company's depot has a lower pH than rainwater collected in the surrounding countryside.

   (a)

   Explain how burning this diesel fuel could cause the rainwater near the depot to be more acidic.

   [3 marks]

   (b)

   The scientists also detect oxides of nitrogen in the exhaust gases from the lorry engines, even though diesel fuel itself contains no nitrogen. Explain how these oxides of nitrogen are formed inside the engine, and describe one environmental problem they cause.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A car manufacturer is deciding whether to develop a new model powered by hydrogen gas instead of continuing to use petrol. The manufacturer asks a team of chemists to evaluate the advantages and disadvantages of using hydrogen rather than petrol as a car fuel, considering combustion products, fuel storage and refuelling infrastructure.

   (a)

   Evaluate the advantages and disadvantages of using hydrogen instead of petrol as a fuel for the new car, considering these factors.

   [6 marks]

   (b)

   The manufacturer's chemists also investigate whether cracking could be used to increase the supply of the smaller hydrocarbons needed to run existing petrol engines, while crude oil supplies are gradually used up. Explain what cracking is, why it is necessary, and describe how the products of cracking a large alkane could be used, referring to homologous series in your answer.

   [6 marks]

   Total for question 4: 12 marks

End of questions