O-LevelChemistryOrganic Chemistry5070/22 · May/June 2022 · Q910 Marks

Alkanes are a homologous series of saturated hydrocarbons.

(a)Draw the structures of two different alkanes with the molecular formula C4H10. Show all of the atoms and all of the bonds in each structure.[2]
(b)State, using the general formula of alkanes, the molecular formula of an alkane which has only 12 carbon atoms in its molecule.[1]
(c)Many alkanes are separated from petroleum (crude oil) by fractional distillation. Describe the fractional distillation of petroleum (crude oil).[3]
(d)(i)Butane, C4H10, reacts with chlorine to give several products. State the condition needed for this substitution reaction.[1]
(d)(ii)One of these products contains 37.8% carbon by mass, 6.30% hydrogen by mass and 55.9% chlorine by mass. Calculate the empirical formula of the product. Deduce the molecular formula of the product.[3]

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Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

[1] [structure 1 for C4H10]
[1] [structure 2 for C4H10]
[1] C12H26
[1] petroleum is heated / petroleum is vapourised / petroleum is at high temperature
[1] use of a (tall fractionating) column
[1] separation depends on boiling point / high boiling point exits from the bottom / low boiling point from the top
[1] UV / sunlight
[1] amount of C is 37.8 / 12 (mol), amount of H is 6.30 / 1 (mol) and of Cl is 55.9/35.5; OR; mole ratio C:H is 3.15 : 6.30 : 1.57
[1] empirical formula is C2H4Cl
[1] molecular formula C4H8Cl2

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