O-LevelChemistryOrganic Chemistry5070/21 · Oct/Nov 2018 · Q411 Marks

The alkanes are a homologous series of saturated hydrocarbons.

(a)(i)Write the general formula for the alkane homologous series.[1]
(a)(ii)Each member of a particular homologous series has the same general formula. Give one other characteristic of a homologous series.[1]
(b)What is the meaning of the term saturated?[1]
(c)Construct the equation for the complete combustion of pentane, C5H12.[2]
(d)Draw the structure of a branched alkane with the formula C5H12. Show all of the atoms and all of the bonds.[1]
(e)Chlorine reacts with pentane. C5H12 + Cl2 → C5H₁₁Cl + HCl
(e)(i)What name is given to this type of chemical reaction?[1]
(e)(ii)What essential condition is needed for chlorine to react with pentane?[1]
(f)A hydrocarbon contains 90% carbon by mass.
(f)(i)Deduce the empirical formula of this hydrocarbon. empirical formula .[2]
(f)(ii)What additional 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] CnH2n+2
[1] Any one from: same functional group (1) similar chemical properties / react similarly (1) trend in physical properties (1) successive members differ by CH2 (1)
[1] all the carbon-carbon bonds are single bonds
[2] C5H12 + 8O2 → 5CO2 + 6H2O correct formulae for reactants and products (1) balanced equation – dependent on formulae (1)
[1] any branched chain isomer of pentane drawn
[1] substitution
[1] light/ uv
[2] mole ratio C = 90/12 AND mole ratio H = 10/1 OR C = 7.5 AND H = 10 (1) empirical formula = C3H4 (1)
[1] (relative) molecular mass

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