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CognitoAlcohols — structure and reactions
Key facts & methods
Alcohol homologous series
- Functional group: -OH (hydroxyl group).
- General formula: CnH(2n+1)OH.
- Methanol CH3OH, Ethanol C2H5OH, Propanol C3H7OH, Butanol C4H9OH.
- Properties change gradually: boiling point increases with chain length.
- All alcohols are soluble in water (due to -OH group). Lower alcohols mix completely.
Production of ethanol
- Fermentation: glucose → ethanol + CO2. Yeast catalyst. ~30°C, anaerobic.
- C6H12O6 → 2C2H5OH + 2CO2
- Advantages: renewable (sugar cane), low temperature, cheap.
- Disadvantages: slow, dilute ethanol produced, batch process.
- Hydration of ethene: C2H4 + H2O → C2H5OH. H3PO4 catalyst, steam, high T and P.
- Advantages: fast, continuous, pure ethanol.
- Disadvantages: uses non-renewable crude oil, high energy cost.
Reactions of alcohols
- Combustion: alcohol + O2 → CO2 + H2O. E.g. C2H5OH + 3O2 → 2CO2 + 3H2O. Clean fuel.
- Oxidation: alcohol + oxidising agent → carboxylic acid. Ethanol + [O] → ethanoic acid.
- Reaction with sodium: alcohol + Na → sodium alkoxide + hydrogen gas. Slower than Na + water.
- Dehydration: alcohol → alkene + water (with concentrated H2SO4 catalyst).
Uses of ethanol
- Fuel (E10 petrol contains 10% ethanol). Burns cleanly.
- Solvent in perfumes, cleaning products, ink.
- Alcoholic drinks (fermentation).
- Hand sanitisers (antiseptic).
- Biofuel — renewable, carbon-neutral in theory (CO2 absorbed by plants during growth).
Exam questions — 4 questions · 10 marks · AQA 8462 style
⚡ Show all working — the AI marks against the AQA mark scheme. Method marks awarded for correct working even if the final answer is wrong.
1 markAlcohol functional groupAQA 8462
What is the functional group in alcohols?
A -COOH (carboxyl group)
B -OH (hydroxyl group)
C -C=C- (double bond)
D -NH2 (amino group)
3 marksFermentation vs hydrationAQA 8462
Compare the production of ethanol by fermentation and by hydration of ethene. Give one advantage and one disadvantage of fermentation. (3 marks)
+30 XP
1 markEthanol combustionAQA 8462
The complete combustion of ethanol produces:
A Carbon monoxide and water
B Carbon dioxide and water only
C Carbon dioxide, water and ethanoic acid
D Carbon and water
4 marksOxidation of ethanolAQA 8462
Describe what happens when ethanol is oxidised. Name the product and write a word equation. How is this relevant to vinegar production? (3 marks)
+40 XP
Module complete! 🎉
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