Ethanol can be made by fermentation of sugars or by the hydration of ethene.
(a) Give two conditions, other than the use of steam, needed for the industrial hydration of ethene. [2]
(b) Give two conditions needed for fermentation. [2]
(c) Give one advantage of making ethanol by fermentation rather than by hydration of ethene. [1]
- (a) any two from: phosphoric acid catalyst (allow H₃PO₄ / phosphoric(V) acid; do not accept 'acid catalyst' alone); (about) 300 °C; (about) 60–70 atm (ignore steam — it is the reactant; ignore 'high temperature' / 'high pressure' without a value)(1)
- (a) second correct condition(1)
- (b) any two from: yeast (allow enzymes in yeast); about 30 °C (allow any temperature from 25 to 40 °C; do not accept 'warm' alone); absence of air / anaerobic (allow no oxygen)(1)
- (b) second correct condition(1)
- (c) uses a renewable raw material / sugars from plants (ethene comes from non-renewable crude oil) (allow lower temperature / lower pressure so less energy needed; ignore 'cheaper' / 'easier' unless qualified)(1)
- Answer: (a) H₃PO₄ catalyst, about 300 °C, 60–70 atm (b) any two of: yeast, about 30 °C, no air (c) renewable raw material
- Examiner tip: 'Fermentation is cheaper' gets no credit — give a specific reason such as a renewable raw material.