O-LevelChemistryOrganic Chemistry5070/22 · May/June 2018 · Q1010 Marks

Ester A has the structure shown. [Figure X.X]

(a)Name ester A.[1]
(b)Ester A reacts with hot aqueous sodium hydroxide to give two compounds, B and C.
(b)(i)Compound B has the percentage composition by mass: 29.3% carbon; 3.7% hydrogen; 39.0% oxygen; 28.0% sodium. Calculate the empirical formula for this compound.[2]
(b)(ii)Compound C has a relative molecular mass of 74 and is oxidised by warm acidified potassium manganate(VII) to give butanoic acid. Suggest a structure for C. Give reasons for your answer.[2]
(c)(i)What is meant by the term isomerism?[1]
(c)(ii)Draw an isomer of ester A.[1]
(d)Explain why ester A is a saturated compound.[1]
(e)Ester A can be used as a fragrance or perfume because it diffuses easily.
(e)(i)Explain why the rate of diffusion of the ester decreases as the temperature decreases.[1]
(e)(ii)Suggest one other use for ester A.[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 (May/June 2018). The mark or mark type is shown in brackets.

[1] 10(a) butyl ethanoate / butyl acetate (1)
[2] 10(b)(i) empirical formula is C2H3O2Na (2) If two marks not scored: 1 mark for mole ratio C: H: O: Na is 2.44: 3.70: 2.44: 1.22 OR 1 mark for C = 29.3/12 H = 3.7/1 O = 39.0/16 Na = 28.0/23
[2] 10(b)(ii) CH3CH2CH2CH2OH (1) idea that it must be an alcohol since it can be oxidised / must be butanol since it is oxidised to butanoic acid (1)
[1] 10(c)(i) (compounds with) the same molecular formula but different structures / (compounds with) the same molecular formula but different arrangements of atoms (1)
[1] 10(c)(ii) any isomer of butyl ethanoate, e.g. CH3CH2CO2CH2CH2CH3 (1)
[1] 10(d) does not contains a carbon-carbon double bond / has only single carbon-carbon bonds (1)
[1] 10(e)(i) molecules move slower / molecules have less kinetic energy (1)
[1] 10(e)(ii) solvent/flavourings (1)

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