O-LevelChemistryOrganic Chemistry5070/22 · May/June 2014 · Q710 Marks

Alkanes are a homologous series of hydrocarbons.

(a)There are two alkanes with the molecular formula C4H10. Draw the structures, showing all the atoms and all the bonds, of these two alkanes. [2][2]
(b)(i)One of the alkanes with the molecular formula C4H10 is butane. Butane is used as a fuel. Construct the equation for the complete combustion of butane. .[1][1]
(b)(ii)Describe one problem associated with the incomplete combustion of butane. .[1][1]
(c)Butane reacts with chlorine in the presence of ultraviolet radiation. Write an equation for this reaction. .[1][1]
(d)(i)Nonane, C9H20, is heated strongly in the presence of a catalyst. Two products are made: an alkane, G, and an alkene, H. Name this type of reaction. .[1][1]
(d)(ii)Alkane G contains 84% carbon by mass. Calculate the molecular formula for G. molecular formula [3][3]
(d)(iii)Suggest a molecular formula for H. .[1][1]

Mark scheme

Marking points from the official mark scheme (May/June 2014). The mark or mark type is shown in brackets.

[1] B7 (a) [Structure for n-butane] H H H H | | | | H–C–C–C–C–H | | | | H H H H (1)
[1] (a) [Structure for isobutane] H H H | | | H–C–C–C–H | | | H H H | C | H (1)
[1] (b) (i) 2C4H10 + 13O2 → 8CO2 + 10H2O (1) ALLOW: correct multiples / fractions IGNORE: state symbols
[1] (b) (ii) Produces carbon monoxide / produces poisonous gas / produces toxic gas / produces lots of soot (1)
[1] (c) C4H10 + Cl2 → C4H9Cl + HCl (1) ALLOW: correct equation with further substitution of H by Cl
[1] (d) (i) Cracking (1)
[1] (d) (ii) (% H is) 16 (%) (1)
[1] (d) (ii) Moles C: 84/12 Moles H: 16/1 or mole ratio 7:16 (1)
[1] (d) (ii) Molecular formula is C7H16 (1)
[1] (d) (iii) C2H4 (1) ALLOW: appropriate formula based on incorrect answer to (c)(ii)

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