O-LevelChemistryOrganic Chemistry5070/21 · May/June 2018 · Q47 Marks

This question is about ethanol and ethanoic acid. [Figure showing structures of ethanol and ethanoic acid]

(a)Describe the manufacture of ethanol by fermentation.[3]
(b)Ethanol can be oxidised by oxygen to form ethanoic acid. Construct the equation for this reaction.[1]
(c)A sample of ethanol is heated with ethanoic acid in the presence of concentrated sulfuric acid catalyst. Draw the structure of the product of this reaction. Show all of the atoms and all of the bonds.[1]
(d)Ethanol is used as a fuel. C2H5OH + 3O2 → 3H2O + 2CO2 The complete combustion of one mole of ethanol releases 1350 kJ of energy. A sample of ethanol reacts with excess oxygen to make 0.240 dm³ of carbon dioxide, measured at room temperature and pressure. Calculate the energy released, in kJ, in this reaction. energy released ..................................................... kJ[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[3] 4(a) use of glucose AND yeast (1) any TWO correct conditions from – aqueous conditions / temperature between 10 and 45 °C / absence of oxygen / any pH between 6 to 8 (1) (fractionally) distil reaction mixture (to get ethanol) (1)
[1] 4(b) CH3CH2OH + O2 → CH3COOH + H2O (1)
[1] 4(c) HO HH H-C-C—O—C—C—H H HH (1)
[2] 4(d) (moles of CO2 = 0.01 so) moles of C2H5OH = 0.005 (1) energy released = (moles of C2H5OH × 1350) = 6.75 (1)

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