1. 1
   A refinery has a surplus of a long-chain hydrocarbon fraction that is in low demand, and wants to convert it into smaller, more useful molecules.

   (a)

   What is meant by 'cracking' of hydrocarbons?

   [1 mark]

   • ABreaking down larger hydrocarbon molecules into smaller, more useful molecules
   • BJoining small hydrocarbon molecules together into larger molecules
   • CRemoving sulfur impurities from crude oil
   • DSeparating crude oil into fractions by boiling point

   (b)

   Which of these is a method used to carry out cracking of hydrocarbons?

   [1 mark]

   • ADissolving the hydrocarbon in water
   • BCooling the hydrocarbon slowly until it solidifies
   • CHeating the hydrocarbon vapour and passing it over a hot catalyst
   • DPassing an electric current through the hydrocarbon

   (c)

   Describe the conditions needed to crack a long-chain hydrocarbon.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemist analyses the products formed when a sample of decane, a long-chain alkane, is cracked in the laboratory.

   (a)

   When a large alkane molecule is cracked, which types of hydrocarbon molecule are typically produced?

   [1 mark]

   • AAn ester and an alcohol
   • BTwo identical alkane molecules only
   • CAn alkene and a carboxylic acid
   • DAn alkane and an alkene

   (b)

   Which general formula applies to the alkene product formed by cracking?

   [1 mark]

   • ACnH2n+2
   • BCnH2n
   • CCnH2n-2
   • DCnHn

   (c)

   Explain why refineries carry out cracking of long-chain hydrocarbon fractions.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A quality control laboratory has been asked to check whether samples of hydrocarbons produced by cracking are saturated or unsaturated.

   (a)

   A technician is given an unknown liquid hydrocarbon and asked to carry out the required practical to test whether it contains a carbon–carbon double bond. Describe how the technician should carry out this test.

   [3 marks]

   (b)

   Describe the expected results of this test and explain how they show whether the hydrocarbon is saturated or unsaturated.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A trainee chemical engineer is being taught why oil refineries crack some of the hydrocarbon fractions obtained from crude oil, and how the products of cracking are identified in the laboratory.

   (a)

   Explain in detail how cracking is carried out, and why it is an important process for oil refineries.

   [6 marks]

   (b)

   Explain how the required practical test for a carbon–carbon double bond can be used to identify and distinguish the products of cracking.

   [6 marks]

   Total for question 4: 12 marks

End of questions