1. 1
   A petrochemical plant heats long-chain alkanes obtained from a heavy fraction of crude oil in the presence of a hot catalyst. This process, called catalytic cracking, breaks the long molecules into shorter, more useful molecules, producing a mixture of smaller alkanes and alkenes.

   (a)

   A petrochemical plant uses catalytic cracking to break down long-chain alkanes from a heavy fraction of crude oil into shorter, more useful molecules, including alkenes. Which general formula correctly represents an alkene, where n is a whole number?

   [1 mark]

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

   (b)

   The plant's chemists test the gas mixture produced by cracking by shaking a sample with orange bromine water. Part of the mixture turns the bromine water colourless. Which type of molecule is responsible for this change, and why does it react in this way?

   [1 mark]

   • AAlkanes, because their single C-C bonds react with bromine in an addition reaction
   • BAlkenes, because their C=C double bond reacts with bromine in an addition reaction
   • CAlkenes, because they are saturated and react with bromine by substitution
   • DAlkanes, because they contain a C=C double bond

   (c)

   One of the reactions occurring in the plant's cracking unit can be summarised as: C12H26 -> C8H18 + C4H8. Explain why this equation is balanced, and identify which product is an alkane and which is an alkene, giving a reason for each.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A food scientist studies ethene gas (C2H4), a hormone that ripens fruit naturally and is also an important feedstock for the chemical industry. She investigates its reactions with steam and with hydrogen under different laboratory conditions.

   (a)

   A food scientist studies ethene gas, which ripens fruit and is also used to make polymers. Ethene reacts with steam in the presence of a phosphoric acid catalyst to produce a useful liquid. What is this product?

   [1 mark]

   • ADichloroethane
   • BEthanoic acid
   • CEthane
   • DEthanol

   (b)

   The scientist then reacts ethene with hydrogen gas in the presence of a nickel catalyst. What type of reaction occurs, and what is the product?

   [1 mark]

   • AAddition reaction, producing ethanol
   • BSubstitution reaction, producing ethane
   • CAddition reaction, producing ethane
   • DCombustion reaction, producing carbon dioxide and water

   (c)

   Describe what happens to the C=C double bond in ethene when it reacts with steam to form ethanol, and state the type of reaction that has occurred.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A car manufacturer relies on a plentiful supply of small alkenes, such as propene and butene, to manufacture plastics for vehicle interiors and other components. However, naturally occurring crude oil fractions mainly contain long-chain alkanes, for which there is comparatively little demand as fuels.

   (a)

   A car manufacturer needs a plentiful supply of small alkenes such as propene and butene to make plastics for vehicle interiors, but naturally occurring crude oil fractions mainly contain long-chain alkanes with little demand as fuels. Explain why cracking is used to solve this problem, and describe the two main conditions under which cracking can be carried out.

   [3 marks]

   (b)

   When decene (C10H20) is cracked, one of the products is octene (C8H16). Write the balanced symbol equation for this cracking reaction and explain, referring to the structure of both molecules, why this reaction is useful to the car manufacturer.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A history teacher explains to students that before large-scale catalytic cracking was developed in the twentieth century, refineries produced far more heavy fuel oil than the transport industry needed, since cars and other vehicles of the time mostly required petrol rather than heavy fuels.

   (a)

   A history teacher explains to students how, before large-scale catalytic cracking was developed in the twentieth century, refineries produced far more heavy fuel oil than the transport industry needed for cars, which mostly required petrol. Explain how cracking helped to solve this economic problem and describe the general conditions used in catalytic cracking, including the physical states of the reactants and products involved.

   [6 marks]

   (b)

   The teacher then asks the students to explain why the alkenes produced by cracking became so economically valuable once industries began manufacturing plastics and other chemicals on a large scale. Explain the differences in reactivity between alkanes and alkenes, and describe how this made alkenes so useful as a feedstock for the chemical industry.

   [6 marks]

   Total for question 4: 12 marks

End of questions