O-LevelChemistryOrganic Chemistry5070/22 · May/June 2020 · Q312 Marks

The table shows some properties of five esters. name | structure | relative molecular mass | melting point /°C | boiling point / °C ---|---|---|---|--- methyl methanoate | HCOOCH3 | 60 | -100 | 32 methyl ethanoate | CH3COOCH3 | 74 | -98 | 57 methyl propanoate | CH3CH2COOCH3 | 88 | -88 | 80 methyl butanoate | CH3CH2CH2COOCH3 | 102 | -95 | 102 methyl pentanoate | CH3CH2CH2CH2COOCH3 | | |

(a)(i)These esters are part of a homologous series. State the relative molecular mass of methyl pentanoate.[1]
(a)(ii)Predict the boiling point of methyl pentanoate ........................................................................................................... °C [1][1]
(a)(iii)Explain why it is not possible to predict the melting point of methyl pentanoate.[1]
(b)At 35°C methyl methanoate is a gas. Explain how the data in the table shows this.[1]
(c)Methyl pentanoate is used to flavour food. Suggest one other use for esters.[1]
(d)(i)Methyl propanoate is prepared by the reaction between propanoic acid and methanol. CH3CH2CO2H + CH3OH ⇌ CH3CH2COOCH3 + H2O The forward reaction is exothermic. Calculate the maximum mass of methyl propanoate that can be made from 11.0g of propanoic acid and excess methanol. Give the answer to three significant figures. mass of methyl propanoate .............................................................. g [2][2]
(d)(ii)The temperature of the reaction mixture is increased. State and explain, in terms of particles, what happens to the rate of the forward reaction.[3]
(d)(iii)The temperature of the reaction mixture is increased. State and explain what happens to the position of the equilibrium.[2]

Mark scheme

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

[1] 3(a)(i) 116 (1)
[1] 3(a)(ii) any value between 115 – 130 (°C) (1)
[1] 3(a)(iii) melting point increases and then decreases / no clear trend (1)
[1] 3(b) 35 °C is greater than the boiling point (1)
[1] 3(c) perfume / solvent (1)
[1] 3(d)(i) moles of propanoic acid = 11.0 / 74 OR 0.149 (1)
[1] 3(d)(i) (mass = 88 × 0.149) = 13.1 (g) (1)
[1] 3(d)(ii) rate of (forward) reaction increases (1)
[1] 3(d)(ii) particles have more kinetic energy / particles moving faster (1)
[1] 3(d)(ii) more successful collisions / more particles with energy equal or above the activation energy (1)
[1] 3(d)(iii) moves to the left / moves to the side of the reactant / moves to side of the alcohol or acid (1)
[1] 3(d)(iii) (forward) reaction is exothermic / backward reaction is endothermic (1)

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