O-LevelChemistryOrganic Chemistry5070/22 · Oct/Nov 2020 · Q58 Marks

Alkenes are made in an oil refinery by cracking hydrocarbons.

(a)(i)Give one other reason why petroleum companies carry out cracking.[1]
(a)(ii)Complete the equation for the cracking of tridecane, C13H28, to form propene, C3H6, and one other hydrocarbon. C13H28 → C3H6 +[1]
(b)(i)Propene is an alkene. Write the general formula for an alkene.[1]
(b)(ii)Propene reacts with steam by an addition reaction. Predict the molecular formula of the product of this reaction.[1]
(b)(iii)When propene undergoes incomplete combustion, a small amount of carbon dioxide is formed. Name two other substances formed when propene undergoes incomplete combustion. and[2]
(c)The structure of propene is shown. [Figure showing the structure of propene] Deduce the partial structure of poly(propene) to show three repeat units.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[1] 5(a)(i) to make petrol / to produce fuels which are needed the most / to make hydrogen
[1] 5(a)(ii) C10H22
[1] 5(b)(i) CnH2n
[1] 5(b)(ii) C3H8O
[1] 5(b)(iii) carbon monoxide (1)
[1] 5(b)(iii) water (1)
[2] 5(c) | CH3 H CH3 H CH3H | -C-C-C-C-C-C- | | | | | | HH HH HH (2) if 2 marks not scored: 1 mark for this structure without extension bonds / 1 mark for this structure terminating with H atom(s) at one or both ends

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