1. 1
   A camping equipment company tests propane, C3H8, as a fuel for portable gas stoves, and compares its chemical behaviour with other hydrocarbons before approving it for sale.

   (a)

   Which statement about propane's bonding is correct?

   [1 mark]

   • AAll the carbon-carbon bonds in propane are single covalent bonds
   • BPropane contains one carbon-carbon double bond
   • CPropane contains an -OH functional group
   • DPropane is a member of the alkene homologous series

   (b)

   The company's chemists note that propane is generally unreactive except in two specific types of reaction. Which pair of reactions are these?

   [1 mark]

   • AAddition with steam and substitution with chlorine
   • BAddition with bromine and combustion
   • CCombustion and substitution with chlorine
   • DNeutralisation and combustion

   (c)

   The chemists carry out a substitution reaction between propane and chlorine gas, exposing the mixture to ultraviolet light. Describe this reaction, including the role of the ultraviolet light and stating the general type of product formed (limited to monosubstitution).

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A team studying air pollution in a busy city monitors emissions from vehicles burning petrol, a mixture of alkanes, in engines with a limited air intake.

   (a)

   Which pair of products is most likely from incomplete combustion of the alkanes?

   [1 mark]

   • AHydrogen and oxygen
   • BCarbon dioxide and water only
   • CSulfur dioxide and water
   • DCarbon monoxide and particulates (carbon)

   (b)

   The team also measures emissions from a small number of vehicles running with a plentiful air supply and efficient engines. Which two products dominate under these complete combustion conditions?

   [1 mark]

   • ACarbon monoxide and hydrogen
   • BCarbon dioxide and water
   • CCarbon and hydrogen
   • DCarbon monoxide and water

   (c)

   State two adverse health or environmental effects associated with the incomplete combustion products identified above.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A safety officer at a chemical storage facility is reviewing why methane, the smallest alkane, is stored separately from more reactive gases despite being flammable. The officer also assesses a nearby cylinder of ethene gas, an alkene, for comparison.

   (a)

   Describe the general reactivity of alkanes towards common reagents such as acids and aqueous bromine, and explain this in terms of their bonding.

   [3 marks]

   (b)

   The officer then tests the cylinder of ethene with aqueous bromine and observes that the orange-brown colour disappears rapidly, unlike with the alkane samples. Explain this difference in terms of the bonding present in alkanes compared with alkenes, and describe the test used to distinguish saturated from unsaturated hydrocarbons.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A rural household relies on a large tank of liquefied petroleum gas (LPG), largely propane and butane, for cooking and heating, since it has no access to mains natural gas.

   (a)

   Explain, in terms of bonding and combustion chemistry, why alkanes such as propane and butane are useful as fuels, and describe the conditions needed to ensure the household burns them as safely and cleanly as possible.

   [6 marks]

   (b)

   A visiting engineer suggests the household switch some appliances to run on a chlorinated derivative of propane instead of propane itself, produced by reacting propane with chlorine gas under ultraviolet light. Explain how this substitution reaction takes place, and discuss why alkanes such as propane otherwise show very limited reactivity compared with unsaturated hydrocarbons.

   [6 marks]

   Total for question 4: 12 marks

End of questions