Alkanes and structural isomerismEdexcel International A Level Chemistry: Subtopic test

1. 1
   Petrol is a mixture of hydrocarbons including pentane, octane and cyclohexane. A refinery chemist classifies each of these compounds as an alkane or a cycloalkane.

   (a)

   What is the molecular formula of octane?

   [1 mark]

   • AC₈H₁₈
   • BC₈H₁₆
   • CC₈H₂₀
   • DC₁₆H₁₈

   (b)

   Which description of cyclohexane is correct?

   [1 mark]

   • AAn unsaturated hydrocarbon containing a C=C bond
   • BA saturated hydrocarbon with general formula CₙH₂ₙ₊₂
   • CA saturated hydrocarbon with general formula CₙH₂ₙ
   • DA hydrocarbon that contains an oxygen atom

   (c)

   Explain what is meant by the terms 'hydrocarbon' and 'saturated' when they are applied to octane.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Pentane, C₅H₁₂, is a liquid in petrol that boils at 36 °C. A refinery sample of C₅H₁₂ is found to contain two other compounds with the same molecular formula, which boil at 28 °C and 10 °C.

   (a)

   Which of these is a structural isomer of pentane?

   [1 mark]

   • AButane
   • BCyclopentane
   • C2-methylpropane
   • D2-methylbutane

   (b)

   What is the IUPAC name of the compound with structural formula C(CH₃)₄?

   [1 mark]

   • A1,1-dimethylpropane
   • B2,2-dimethylpropane
   • CPentane
   • D2-methylbutane

   (c)

   Explain why the compound that boils at 28 °C, 2-methylbutane, is a structural isomer of pentane.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A hydrocarbon X is found in petrol. Analysis shows that it contains 83.3% carbon and 16.7% hydrogen by mass, and its relative molecular mass is 72.0. X does not decolourise bromine water and contains no carbon–carbon double bonds.

   (a)

   Use the data to deduce the empirical formula and the molecular formula of X, showing your working.

   [3 marks]

   (b)

   State what the formula of X shows about the type of compound, and give the name and structural formula of each of its structural isomers.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Hexane, C₆H₁₄, and cyclohexane, C₆H₁₂, are both found in petrol. Hexane has five structural isomers, which a student is trying to identify systematically.

   (a)

   Explain why hexane and cyclohexane are both saturated hydrocarbons, but are not isomers of each other, and why cyclohexane has two fewer hydrogen atoms than hexane.

   [6 marks]

   (b)

   Describe a systematic method the student could use to find all five structural isomers of hexane, giving the name of each isomer.

   [6 marks]

   Total for question 4: 12 marks

End of questions