1. 1
   A market gardener notices that ripening fruit, such as bananas, releases a gas called ethene, which is a member of the alkene homologous series with the general formula CnH2n.

   (a)

   What is the molecular formula of ethene, which has two carbon atoms?

   [1 mark]

   • AC2H6
   • BC2H4
   • CC2H2
   • DC3H6

   (b)

   The gardener wants to test whether the gas released is an alkene. Which test correctly distinguishes an alkene such as ethene from an alkane?

   [1 mark]

   • AAdding the gas to bromine water; an alkene rapidly decolourises it while an alkane does not
   • BAdding the gas to bromine water; an alkane rapidly decolourises it while an alkene does not
   • CMeasuring the density of the gas, since alkenes are always denser than alkanes
   • DBurning the gas, since only alkenes produce carbon dioxide and water

   (c)

   Explain, in terms of bonding, why ethene is classified as an unsaturated hydrocarbon.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A food scientist bubbles a hydrocarbon gas through orange bromine water in a test tube, and the bromine water rapidly turns colourless.

   (a)

   What can be concluded from this observation?

   [1 mark]

   • AThe gas is an alkane, since alkanes react with bromine water
   • BNo conclusion can be drawn from this test
   • CThe gas is carbon dioxide, which always decolourises bromine water
   • DThe gas is an alkene, since it contains a carbon-carbon double bond that reacts with bromine

   (b)

   The food scientist identifies the gas as but-1-ene, an alkene with four carbon atoms. Which of these is the correct molecular formula for but-1-ene?

   [1 mark]

   • AC4H6
   • BC4H10
   • CC4H8
   • DC3H6

   (c)

   Describe the product formed when but-1-ene reacts with bromine water, and name the type of reaction that takes place.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A plastics manufacturer reacts propene, an alkene with three carbon atoms, with bromine in a sealed reaction vessel.

   (a)

   Describe, in words, the structural formula of propene and explain how its structure allows it to react with bromine.

   [3 marks]

   (b)

   Name the product formed when propene reacts with bromine, and explain what this reaction demonstrates about the difference between alkenes and alkanes.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school laboratory technician is asked to design a simple experiment that a class of students could use to distinguish between two colourless, unlabelled gas samples, one of which is an alkane and the other an alkene, without using any expensive or specialist equipment.

   (a)

   Describe how bromine water could be used to distinguish between the two gases, and explain the chemical reason why the results differ.

   [6 marks]

   (b)

   Evaluate why bromine water is considered a reliable and practical test for identifying unsaturation in a hydrocarbon, considering both the chemistry involved and the practicality of carrying out the test in a school laboratory.

   [6 marks]

   Total for question 4: 12 marks

End of questions