O-LevelChemistryOrganic Chemistry5070/21 · Oct/Nov 2016 · Q311 Marks

The alcohols are a homologous series with the general formula CnH2n+1OH. (a) Deduce the molecular formula of the alcohol having eight carbon atoms. (b) The table shows some information about different alcohols. alcohol | formula | melting point /°C | boiling point /°C | density in g/cm³ ---|---|---|---|--- ethanol | C2H5OH | -117 | 79 | 0.789 propanol | C3H7OH | -126 | 98 | 0.804 butanol | C4H9OH | -89 | 117 | pentanol | C5H11OH | -79 | 138 | 0.815 hexanol | C6H13OH | -47 | 158 | 0.820

(a)Deduce the molecular formula of the alcohol having eight carbon atoms.[1]
(b)(i)Describe how the boiling point changes with the number of carbon atoms in the alcohol.[1]
(b)(ii)Estimate the density, in g/cm³, of butanol.[1]
(b)(iii)What is the physical state of pentanol at room temperature and pressure? Explain your answer.[1]
(c)How does viscosity change in the homologous series of alcohols? Explain your answer.[2]
(d)Construct the equation for the complete combustion of propanol.[2]
(e)(i)Propanol can be oxidised to propanoic acid. Suggest the oxidising agent and describe the conditions used for this reaction.[2]
(e)(ii)Draw the structure of propanoic acid, showing all the atoms and all the bonds.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2016). The mark or mark type is shown in brackets.

[1] C8H18O (1)
[1] increases with increased number of carbon atoms (1)
[1] values between 0.806 and 0.813 (inclusive) (1)
[1] liquid because melting point is below room temperature and boiling point is above room temperature (1)
[1] (viscosity) increases as number of C atoms increases/increases down the alcohols (1)
[1] any correct answer related to length/size/mass of molecule e.g. size of molecule increases/length of carbon chain increases/chains get more tangled/van der Waals' forces increase/intermolecular forces increase (1)
[1] C3H7OH + 4½O2 → 3CO2 + 4H2O
[1] correct formulae for reactants and products (1)
[1] correct balancing, dependent on correct formulae (1)
[1] (acidified) potassium manganate(VII)/potassium permanganate (1)
[1] heat/reflux (1)
[1] H | H-C-H | H-C-H | H-C(=O)OH (1) (representing CH3CH2COOH structure)

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