CIE iGCSE Co-Ordinated Science C11.3 Fuels Exam Style Questions Paper 3
Question
Useful hydrocarbons are obtained from petroleum.
(a) Fig. 11.1 shows the industrial process used to separate useful hydrocarbons from petroleum.
(i) Name this process shown in Fig. 11.1.
(ii) State if chemical changes or physical changes are involved when useful hydrocarbons are obtained from petroleum in this process. Explain your answer.
(iii) Refinery gas and bitumen are obtained from petroleum. State one use of refinery gas and one use of bitumen.
(b) Explain why the measurement of boiling temperature can be used to find out whether a liquid is a pure alkane or a mixture of alkanes.
(c) Methane and ethane are gaseous alkanes.
(i) Complete the dot-and-cross diagram of a molecule of methane. In your diagram, show:
- the chemical symbols of the elements
- the arrangement of the outer shell electrons.
(ii) State why ethane is a saturated hydrocarbon.
(iii) State the name of the unsaturated hydrocarbon that has only two carbon atoms in each of its molecules.
▶️Answer/Explanation
11 (a) (i) The process shown in Fig. 11.1 is fractional distillation.
11 (a) (ii) Physical changes are involved in this process. This is because the separation of hydrocarbons is based on their different boiling points, which is a physical property. No new substances are formed during fractional distillation.
11 (a) (iii)
- Refinery gas is used for heating and cooking.
- Bitumen is used for surfacing roads and waterproofing.
11 (b) The measurement of boiling temperature can be used to determine whether a liquid is a pure alkane or a mixture of alkanes because a pure substance has a single, sharp boiling point, whereas a mixture of alkanes will have a range of boiling points due to the different boiling points of the individual components.
11 (c) (i) The dot-and-cross diagram for methane (CH4) should show:
- One carbon atom with four outer shell electrons (dots or crosses).
- Four hydrogen atoms, each with one outer shell electron (dots or crosses).
- Each hydrogen atom shares one electron with the carbon atom, forming four single covalent bonds.
11 (c) (ii) Ethane is a saturated hydrocarbon because it contains only single covalent bonds between carbon atoms, meaning it has the maximum number of hydrogen atoms bonded to the carbon atoms.
11 (c) (iii) The unsaturated hydrocarbon with only two carbon atoms in each molecule is ethene (C2H4).