O-LevelChemistryOrganic Chemistry5070/22 · Oct/Nov 2018 · Q411 Marks

The alkenes are a homologous series of unsaturated hydrocarbons.

(a)Describe two characteristics of a homologous series. 1. .......... 2. ..........[2]
(b)Construct the equation for the complete combustion of butene, C₄H₈.[2]
(c)Draw the structure of a branched alkene with the formula C₄H₈. Show all of the atoms and all of the bonds.[1]
(d)Butene reacts with hydrogen in the presence of nickel.
(d)(i)Name the product formed.[1]
(d)(ii)What is the purpose of the nickel?[1]
(d)(iii)State one other condition needed for this reaction.[1]
(e)A hydrocarbon contains 85.7% carbon by mass.
(e)(i)Deduce the empirical formula of this hydrocarbon.[2]
(e)(ii)What other piece of information is needed to deduce the molecular formula of this hydrocarbon?[1]

Mark scheme

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

[1] (a) Any two from: same functional group (1)
[1] (a) same general formula (1)
[1] (a) similar chemical properties / react similarly (1)
[1] (a) trend in physical properties (1)
[1] (a) successive members differ by CH2 (1)
[2] (b) C4H8 + 6O2 → 4CO2 + 4H2O (2)
[1] (b) 1 mark for correct reactants and products if equation not balanced
[1] (c) structure of 2-methylpropene drawn showing all atoms and all bonds
[1] (d)(i) butane
[1] (d)(ii) catalyst / to speed up the reaction / to increase the rate of reaction
[1] (d)(iii) heat / high temperature
[1] (e)(i) mole ratio C = 85.7 / 12 AND mole ratio H = 14.3 / 1 OR C = 7.14 AND H = 14.3 (1)
[1] (e)(i) empirical formula = CH2 (1)
[1] (e)(ii) (relative) molecular mass

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