O-LevelChemistryOrganic Chemistry5070/22 · May/June 2019 · Q48 Marks

Petroleum (crude oil) is an important source of many chemicals.

(a)Outline the separation of petroleum (crude oil) into fractions such as petrol, diesel and bitumen.[3]
(b)State one large scale use of bitumen.[1]
(c)(i)Long chain hydrocarbons can be cracked to produce hydrogen. (i) A long chain hydrocarbon has the molecular formula C12H26. Explain how the formula shows that this hydrocarbon is an alkane.[1]
(c)(ii)Construct an equation to show the cracking of C12H26 to make hydrogen and at least one alkene.[1]
(d)Hydrogen and petrol are both used as fuels. State and explain one advantage of using hydrogen rather than petrol as a fuel.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.

[3] 4(a) One mark each for any three of: • fractional distillation • petroleum is heated / petroleum vaporised (into column) • idea of components / fractions with different boiling points • (fractions with) low boiling point come off at the top / (fractions with) high boiling point come off at the bottom / fractions come off at different levels (in the column)
[1] 4(b) (surfacing) roads / (water-proofing) roofs
[1] 4(c)(i) idea that the formula fits CnH2n+2 e.g. for C12H26 n=12 and 2n+2 is 26
[1] 4(c)(ii) correct balanced equation e.g. C12H26 → C12H24 + H2 OR C12H26 → H2 + 3C4H8 etc.
[2] 4(d) (hydrogen) does not form carbon dioxide (1) so does not lead to greenhouse effect / flooding / drought / climate change (1) OR water is the only product (1) so does not lead to greenhouse effect / flooding / drought / climate change (1) OR (hydrogen) renewable / sustainable (1) hydrogen is not finite (resource) / (the product water) can be split up (or electrolysed) to give hydrogen / hydrogen can be formed again from water (1)

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