1. 1
   A student is given a sample of pentane, an unbranched-chain alkane, and asked to write its molecular formula using the general formula for alkanes, CnH(2n+2).

   (a)

   What is the molecular formula of pentane?

   [1 mark]

   • AC5H12
   • BC5H10
   • CC5H8
   • DC4H10

   (b)

   The student then mixes a sample of pentane with chlorine gas and exposes the mixture to ultraviolet radiation. A reaction occurs. What type of reaction takes place, and what feature of alkanes explains why this reaction is possible?

   [1 mark]

   • AAn addition reaction, because alkanes contain a carbon-carbon double bond
   • BA combustion reaction, because chlorine acts as an oxidising fuel
   • CA substitution reaction, because a hydrogen atom is replaced by a chlorine atom
   • DA substitution reaction, because alkanes contain a carbon-carbon double bond

   (c)

   Explain why pentane is classified as a saturated hydrocarbon.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemistry teacher shows the class a model of butane and asks them to identify the correct displayed formula. Butane is an unbranched-chain alkane with four carbon atoms.

   (a)

   How many hydrogen atoms does one molecule of butane contain?

   [1 mark]

   • A8
   • B10
   • C12
   • D14

   (b)

   The teacher then asks the class to name the alkane that has three carbon atoms fewer than butane. What is the correct name?

   [1 mark]

   • AEthane
   • BPentane
   • CPropane
   • DMethane

   (c)

   Draw out in words the structural formula of butane, describing how the carbon and hydrogen atoms are arranged along the unbranched chain.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A laboratory technician mixes methane gas with chlorine gas in a clear glass flask and leaves it on a sunlit windowsill. After some time, a reaction occurs and the mixture turns from yellow-green towards colourless, with steamy fumes forming.

   (a)

   Explain what causes this reaction to begin, referring to the conditions required.

   [3 marks]

   (b)

   Describe the products formed in this mono-substitution reaction between methane and chlorine, and name the type of reaction that has occurred.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A materials science student is comparing the properties of alkanes of different chain lengths, from methane (one carbon atom) up to pentane (five carbon atoms), all of which are saturated hydrocarbons belonging to the same homologous series.

   (a)

   Explain what is meant by the term 'homologous series' and describe, with reasons, how the physical properties of these alkanes change as the chain length increases.

   [6 marks]

   (b)

   Evaluate why alkanes, despite containing only single covalent bonds, are still able to react with halogens such as chlorine under ultraviolet radiation, and explain why this reaction is described as mono-substitution rather than addition.

   [6 marks]

   Total for question 4: 12 marks

End of questions