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Home › GCSE/IGCSE Notes › IGCSE Chemistry › Ethanol

Simple Explanation of Ethanol

Ethanol is a chemical compound. When people refer to it, they often name it simply as alcohol. The familiar alcohol in drinks is C2H5OH or C2H60 (CH3-CH2-OH), and should properly be called ethanol.
CH3–CH2–OH indicates the carbon of a methyl group (CH3–) is attached to the carbon of a methylene group (–CH2–), which is attached to the oxygen of a hydroxyl group (–OH).

Topics covered on this page (Ethanol):
Manufacture of ethanol
Fermentation of sugar
Hydration of ethene

Manufacture of ethanol

Ethanol is manufactured by two different processes:
  1. Fermentation of sugar
  2. Hydration of ethene

Fermentation of sugar

  • Dissolve sugar/starch in water and add yeast to this solution.
  • Leave the mixture to ferment in warm conditions (25-40°C) for several days in the absence of air (anaerobic conditions, which means without oxygen present).
  • Enzymes (biological catalysts) in the yeast convert the sugar into ethanol and carbon dioxide. This process is called fermentation. 
  • Filter off the excess yeast to obtain a dilute solution of ethanol.
If the ethanol content in the solution rises to around 15%, the yeast is killed, so it is impossible to make pure alcohol by fermentation. If a more concentrated solution of ethanol is required it is purified through fractional distillation. Fractionally distilling the ethanol takes advantage of the difference in boiling point between ethanol and water. Water boils at 100°C while ethanol boils at  78°C. The liquid distilling at 78°C is 96% pure ethanol, it is impossible to get it to 100% because the rest is water and this cannot be removed by simple distillation.

Whatever the starting point, sugar or starch, the enzymes in the yeast produce glucose, C6H12O6. The enzymes in yeast then convert the glucose into ethanol:
Picture

Hydration of ethene

Ethanol can also be made by reacting ethene with steam. This process is called hydration.
  • Mixture of ethene and steam is passed over a phosphoric acid catalyst at a temperature of 300°C and 60-70 atmospheres of pressure.
  • The ethanol is condensed as a liquid.
  • The ethene required for this reaction is obtained from crude oil.

Related Study Revision Notes

Organic Chemistry
Alkanes
Alkenes
‹ IGCSE Chemistry Topics
‹ GCSE/IGCSE Subjects
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