O-LevelChemistryOrganic Chemistry5070/22 · May/June 2018 · Q510 Marks

Naphtha is a fraction obtained from petroleum (crude oil).

(a)Explain how naphtha is obtained from petroleum (crude oil).[3]
(b)One compound in the naphtha fraction has the formula C12H26
(b)(i)From this formula, how can you deduce that this compound is an alkane?[1]
(b)(ii)The alkane, C12H26, can be cracked to form an alkene that has six carbon atoms per molecule. Construct the equation for this reaction.[2]
(c)Ethene, C2H4, can be made by cracking hydrocarbons. Draw a 'dot-and-cross' diagram for ethene. You only need to show the outer shell electrons.[2]
(d)Chlorine reacts with both ethene and ethane.
(d)(i)One molecule of ethene reacts with one molecule of chlorine. Draw the structure of the product of this reaction. Show all of the atoms and all of the bonds.[1]
(d)(ii)One molecule of ethane can react with two molecules of chlorine. What is the molecular formula of the organic product of this reaction?[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[3] 5(a) petroleum is heated / crude oil is heated (1) fractional distillation / fractionating column (1) idea that separation works because naphtha has different boiling point to other fractions / idea of different boiling points at different places in the column / naphtha comes off at particular height in the column (1)
[1] 5(b)(i) (molecular formula) fits the (general) formula CnH2n+2 (1)
[2] 5(b)(ii) C12H26→ C6H12 + C6H14/C12H26 → 2C6H12 + H2 formula for C6H12 (1) equation balanced dependent on alkene formula (1)
[2] 5(c) [Figure for ethene dot-and-cross diagram, 2 marks] If 2 marks not obtained, one mark for: EITHER two shared pairs of electrons between the two carbon atoms OR incorrect number of electrons in carbon-carbon bond (or bond shown by line) BUT one electron pair between each of the two carbon-hydrogen atoms on each of the two carbon atoms (four electron pairs)
[1] 5(d)(i) [Figure for 1,2-dichloroethane structure, 1 mark]
[1] 5(d)(ii) C2H4Cl2 (1)

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