O-LevelChemistryOrganic Chemistry5070/22 · May/June 2016 · Q36 Marks

Esters are used as food flavourings and solvents.

(a)Draw the structure of ethyl methanoate, showing all of the atoms and all of the bonds.[1]
(b)(i)Ethyl ethanoate evaporates at room temperature. What is meant by the term evaporation?[1]
(b)(ii)A sample of ethyl ethanoate in a beaker is moved into a colder room. Explain, in terms of the kinetic particle theory, why this results in a decrease in the rate of evaporation.[2]
(b)(iii)The table shows some information about different esters. name structure relative molecular mass (Mᵣ) methyl ethanoate CH3CO2CH3 74 ethyl ethanoate CH3CO2C2H5 88 propyl ethanoate CH3CO2C3H7 102 butyl ethanoate CH3CO2C4H9 116 pentyl ethanoate CH3CO2C5H11 130 Which ester has the lowest rate of evaporation at room temperature and pressure? Explain your answer.[2]

Mark scheme

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

[1] H-C(=O)-O-CH2-CH3 (structure showing all atoms and bonds)
[1] Changing of a liquid into a gas/changing liquid to vapour (happening at any temperature)
[1] Molecules have less energy/molecules move slower
[1] Molecules don't have enough energy to overcome force between molecules/molecules don't have enough energy to escape (into the air)
[1] Pentyl ethanoate/CH3CO2C5H11
[1] Highest relative formula mass

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