Alcohols
7 marks · HardThe table shows two industrial methods for producing ethanol: hydration of ethene and fermentation of glucose.
State the temperature, pressure and catalyst required for the hydration of ethene to make ethanol.
Compare the energy requirements for the hydration of ethene and fermentation methods. Give one reason for the difference.
State one advantage and one disadvantage of the hydration method compared to fermentation.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Temperature: 300°C; Pressure: 60–70 atm; Catalyst: phosphoric acid · must show all three conditions, correct values
(b) Hydration needs more energy (higher temperature and pressure); fermentation uses milder conditions (lower temperature/atmospheric pressure) because enzymes in yeast work best at lower temperatures. · must show comparison and correct reason
(c) Advantage: Hydration is faster/continuous/purer ethanol; Disadvantage: Hydration uses non-renewable resources/high energy · must show one valid advantage and one disadvantage
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct temperature (300°C)
B2 (a) · 1 mark · Correct pressure (60–70 atm)
B3 (a) · 1 mark · Correct catalyst (phosphoric acid)
B4 (b) · 1 mark · Hydration has higher energy needs / fermentation lower
B5 (b) · 1 mark · Reason related to process conditions (temperature/pressure or catalyst requirements)
B6 (c) · 1 mark · Valid advantage of hydration compared to fermentation
B7 (c) · 1 mark · Valid disadvantage of hydration compared to fermentation
Worked solution
a) Temperature: 300°C; Pressure: 60–70 atmospheres; Catalyst: phosphoric acid (H3PO4)
b) Hydration of ethene uses much more energy than fermentation because it needs high temperature and pressure, while fermentation occurs at room temperature and pressure. Enzymes used in fermentation work best at much lower temperatures.
c) An advantage of hydration compared to fermentation is that it is much faster and produces purer ethanol continuously. A disadvantage is that it uses non-renewable crude oil resources and is energy intensive.