1. 1
   A student has four sealed gas jars, each containing a different unbranched-chain alkane: methane, ethane, propane and butane. She burns a small sample of each in a plentiful supply of oxygen and collects the products for testing.

   (a)

   Which general formula represents the homologous series of the alkanes?

   [1 mark]

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

   (b)

   Which statement correctly explains why alkanes are described as saturated hydrocarbons?

   [1 mark]

   • AEach molecule contains at least one carbon-carbon double bond
   • BEach carbon atom in the chain forms single covalent bonds only, with no carbon-carbon double bonds
   • CEach molecule contains an -OH functional group
   • DEach molecule can dissolve an unlimited amount of water

   (c)

   State the two products formed when butane, C4H10, undergoes complete combustion in a plentiful supply of oxygen.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A technician is given two unlabelled gas jars, one containing propane (an alkane) and one containing propene (an alkene). She adds a few drops of orange bromine water to a sample of gas from each jar and shakes gently.

   (a)

   What colour change would be observed when orange bromine water is shaken with a sample of propene gas?

   [1 mark]

   • ANo colour change occurs
   • BColourless to orange
   • CPurple to colourless
   • DOrange to colourless

   (b)

   Which functional group in the propene molecule is responsible for the colour change with bromine water?

   [1 mark]

   • AA -COOH group
   • BAn -OH group
   • CA carbon-carbon double bond (C=C)
   • DSingle carbon-carbon bonds only

   (c)

   Explain, in terms of molecular structure, why propane produces no colour change with bromine water while propene decolourises it.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A chemist reacts a sample of ethene gas, C2H4, with bromine, Br2, in an addition reaction to form a saturated product. She then repeats a similar reaction using but-1-ene, C4H8, an alkene with a double bond between the first and second carbon atoms of an unbranched chain.

   (a)

   Describe the addition reaction that occurs between ethene, C2H4, and bromine, Br2, including the name and molecular formula of the product formed.

   [3 marks]

   (b)

   Predict the molecular formula of the product formed when but-1-ene reacts completely with bromine, and explain why but-2-ene (an alkene with the same molecular formula but the double bond between the second and third carbon atoms) would react with bromine in exactly the same way.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemicals company plans to use ethene and propene, both alkenes, as feedstocks to manufacture dibromo-addition products for further industrial processing. As the consulting chemist, you must explain the underlying reaction chemistry to the production team.

   (a)

   A fuel company is testing a new hydrocarbon fuel blend and wants its engineers to understand the difference between alkanes and alkenes before marketing its 'unsaturated content'. Explain, in detail, the structural difference between alkanes and alkenes, how this difference can be identified experimentally using a chemical test, and how each type of hydrocarbon behaves when burned completely in a plentiful supply of oxygen.

   [6 marks]

   (b)

   Explain the mechanism and outcome of reacting ethene and propene separately with bromine, including the name or formula of each product formed, and explain why both alkenes, despite being different members of the same homologous series, react with bromine in the same way.

   [6 marks]

   Total for question 4: 12 marks

End of questions