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Making and oxidising ethanol
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Ethanol can be made from ethene or by fermentation. It can be oxidised in three ways.
Oxidising ethanol
Burning in air or oxygen (complete combustion): C2H5OH + 3O2 → 2CO2 + 3H2O
Microbial oxidation: microorganisms use oxygen from the air to turn ethanol into ethanoic acid. This is why wine left open turns sour (vinegar).
Potassium dichromate(VI) in dilute sulfuric acid, heated, oxidises ethanol to ethanoic acid. The solution changes from orange to green.
Microbial oxidation: microorganisms use oxygen from the air to turn ethanol into ethanoic acid. This is why wine left open turns sour (vinegar).
Potassium dichromate(VI) in dilute sulfuric acid, heated, oxidises ethanol to ethanoic acid. The solution changes from orange to green.
Two ways to make ethanol
Why those fermentation conditions?
No air: with oxygen, the ethanol would be oxidised to ethanoic acid, and yeast would respire aerobically instead of making ethanol.
Optimum temperature: below it the reaction is too slow; above it the enzymes in yeast are denatured.
Optimum temperature: below it the reaction is too slow; above it the enzymes in yeast are denatured.
Give one advantage and one disadvantage of making ethanol by fermentation rather than from ethene.
- Advantage: uses a renewable raw material (sugar from crops).
- Disadvantage: slow, batch process giving impure ethanol that must be distilled.
Answer: Renewable raw material; but slow and the ethanol is impure.
Ethanol is oxidised by burning, by microbes (to ethanoic acid) and by acidified potassium dichromate(VI) (orange to green). It is made from ethene and steam (phosphoric acid, 300 °C, 60 to 70 atm) or by fermenting glucose with yeast (no air, about 30 °C).
The interactive lesson includes the diagrams for this topic.
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