O-LevelChemistryOrganic Chemistry5070/21 · May/June 2020 · Q412 Marks

The table shows some properties of five esters. | name | structure | relative molecular mass | melting point /°C | boiling point /°C | |---|---|---|---|---| | methyl ethanoate | CH3COOCH3 | 74 | -98 | 57 | | ethyl ethanoate | CH3COOCH2CH3 | 88 | -84 | 77 | | propyl ethanoate | CH3COOCH2CH2CH3 | 102 | -95 | 102 | | butyl ethanoate | CH3COOCH2CH2CH2CH3 | 116 | -78 | 126 | | pentyl ethanoate | CH3COOCH2CH2CH2CH2CH3 | 130 | -71 | 148 |

(a)These esters are part of a homologous series. State two characteristics of a homologous series.[2]
(b)The next member of the homologous series is hexyl ethanoate. Explain why it is more difficult to predict the melting point than the boiling point of hexyl ethanoate.[1]
(c)At 25°C ethyl ethanoate is a liquid. Explain how the data in the table shows this.[1]
(d)State one use for an ester.[1]
(e)(i)Propyl ethanoate is prepared by the reaction between ethanoic acid and propanol. CH3CO2H + CH3CH2CH2OH <=> CH3COOCH2CH2CH3 + H2O Calculate the maximum mass of propyl ethanoate that can be made from 7.20g of ethanoic acid and excess propanol. Give your answer to three significant figures. mass of propyl ethanoate ................................................................ g[2]
(e)(ii)The concentration of ethanoic acid is increased. State and explain, in terms of particles, what happens to the rate of the forward reaction.[3]
(e)(iii)The water formed in the reaction is removed. State and explain what happens to the position of the equilibrium.[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[2] Any two from: general formula (1); same or similar chemical properties (1); same functional group (1); physical properties show a trend (1); each member varies by a CH2 group / each member varies by 14 amu (1)
[1] melting point increases and then decreases but boiling point just increases / melting point goes up then down, but boiling point has a trend
[1] melting point below 25°C and boiling point above 25°C / 25°C is between melting point and boiling point
[1] perfume / solvent / flavouring
[2] mole ethanoic acid = 7.20/60 OR 0.12 (1) (mass = 102 × 0.12) = 12.2 (g) (1)
[3] rate increases (1) particles more crowded together / particles are closer together / more particles per unit volume (1) more collisions per second / greater collision frequency (1)
[2] moves to the right / moves to the side of the product / moves to side of the ester (1) to replace water that has been removed (1)

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