1. 1
   A student tests an unknown gas sample obtained from cracking a long-chain hydrocarbon, using bromine water to determine whether the gas is saturated or unsaturated.

   (a)

   A student adds an unknown gas sample from cracking to orange bromine water and shakes it. The bromine water turns colourless. What does this show about the gas?

   [1 mark]

   • AThe gas is a saturated alkane
   • BThe gas is an unsaturated alkene
   • CThe gas is pure oxygen
   • DThe gas is carbon dioxide

   (b)

   Which feature of the gas's molecules causes it to react with and decolourise bromine water?

   [1 mark]

   • AA single covalent bond between carbon atoms
   • BA high boiling point
   • CThe presence of hydrogen atoms
   • DA carbon–carbon double bond

   (c)

   Describe what the student observes in this test and state the conclusion that can be drawn about the unknown gas.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A laboratory assistant labels two unlabelled gas cylinders using their molecular formulae, C2H4 and C3H6, and must identify each alkene.

   (a)

   Which alkene has the molecular formula C2H4?

   [1 mark]

   • AEthene
   • BMethane
   • CPropene
   • DEthane

   (b)

   Which alkene has the molecular formula C3H6?

   [1 mark]

   • AEthene
   • BPropane
   • CPropene
   • DButene

   (c)

   Explain how an alkene such as ethene or propene can be recognised from its name or molecular formula.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A fuel supplier is testing several samples produced by cracking to decide which ones are suitable to sell as fuels.

   (a)

   A fuel supplier tests a sample of a cracking product with bromine water and finds that the bromine water stays orange. Describe what this result shows about the sample and how the test was carried out.

   [3 marks]

   (b)

   Explain why some products of cracking, particularly the saturated alkanes, are useful as fuels.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school science department is developing a practical demonstration to show students how cracking produces both saturated and unsaturated hydrocarbons, and how these can be identified and used.

   (a)

   Explain, in full, how the bromine water test is carried out and how the results distinguish between saturated and unsaturated hydrocarbons.

   [6 marks]

   (b)

   Discuss the role that products of cracking play in meeting the demand for fuels, referring to saturation, the bromine water test, and why some products are more suitable as fuels than others.

   [6 marks]

   Total for question 4: 12 marks

End of questions