Alcohols Cambridge IGCSE Chemistry (9–1) revision
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In plain words
Ethanol is the alcohol in drinks, and also a fuel and a solvent. It can be made the way people have made it for thousands of years, by letting yeast feed on sugar, or the modern way, by reacting ethene from crude oil with steam.
Three things to know
- Fermentation: glucose solution with yeast, at about 30 °C with no air. C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.
- Hydration of ethene: ethene and steam at about 300 °C and 60 atmospheres (6000 kPa) with an acid catalyst. C₂H₄ + H₂O → C₂H₅OH.
- Fermentation uses a renewable raw material but is slow and makes impure ethanol. Hydration is fast and makes pure ethanol, but the ethene comes from crude oil. Ethanol burns to carbon dioxide and water, and can be oxidised to ethanoic acid.
Tips and tricks
- Fermentation needs three things: yeast, warmth (about 30 °C) and no oxygen. Too hot and the yeast's enzymes stop working.
- Compare the two methods point for point: raw material, speed, purity.
It lands in your notebook with its questions as flashcards.
Alcohols: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is the functional group of the alcohols?
Every alcohol has an –OH group.
Which living thing is used to make ethanol by fermentation?
Its enzymes turn glucose into ethanol.
What is the other product of fermentation, besides ethanol?
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.
What is made when ethene reacts with steam?
Water adds across the double bond.
What is the formula of ethanol?
Two carbon atoms and an –OH group.
Which is a use of ethanol?
It burns cleanly and dissolves many substances.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
4 questions, 9 marks. Write your answers on paper, then check them.
Alcohols
Cambridge IGCSE Chemistry (9–1) 0971 · 9 marks · papermunch.org
Name ______________________________ Date ______________
State three conditions needed to make ethanol by fermentation.[3]
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Any three: yeast; a temperature of about 30 °C (25 to 35 °C); no oxygen (anaerobic); glucose (sugar) in solution.
Give one advantage and one disadvantage of making ethanol by fermentation rather than from ethene.[2]
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Advantage: it uses a renewable raw material (sugar from plants), or needs little energy. Disadvantage: it is slow, or the ethanol is impure and has to be distilled.
Write the balanced equation for the complete combustion of ethanol.[2]
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C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.
Explain why fermentation is not carried out at 60 °C.[2]
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The enzymes in the yeast would be denatured (the yeast would be killed), so fermentation would stop.
Answers: Alcohols
- 1. Any three: yeast; a temperature of about 30 °C (25 to 35 °C); no oxygen (anaerobic); glucose (sugar) in solution.
- 2. Advantage: it uses a renewable raw material (sugar from plants), or needs little energy. Disadvantage: it is slow, or the ethanol is impure and has to be distilled.
- 3. C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.
- 4. The enzymes in the yeast would be denatured (the yeast would be killed), so fermentation would stop.