Who this is for: Cambridge IGCSE Chemistry (0620) students who want alcohols — ethanol, fermentation and oxidation — to become linked process answers instead of isolated “–OH group” facts.
What query it owns: how to understand and revise alcohols in Cambridge IGCSE Chemistry.
Why this is safe: this page owns the alcohols revision-guide angle, while Tutopiya’s Alcohols subtopic page owns the learning resource and the free Alcohols quiz owns the practice.

Alcohols contain the –OH functional group and form the homologous series with general formula CₙH₂ₙ₊₁OH. Cambridge IGCSE Chemistry (0620) focuses on ethanol — its manufacture by fermentation and by hydration of ethene, its combustion, and its oxidation to ethanoic acid. Exam answers must include conditions for each process and balanced equations where required. This guide covers the syllabus reactions, comparisons and typical past-paper stems.

Key takeaways

• Alcohols have general formula CₙH₂ₙ₊₁OH; ethanol is C₂H₅OH.
• Fermentation: glucose → ethanol + CO₂, yeast enzyme, ~35 °C, anaerobic.
• Hydration of ethene: ethene + steam → ethanol, H₃PO₄ catalyst, 300 °C, 60 atm.
• Combustion of ethanol: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.
• Oxidation of ethanol (acidified K₂Cr₂O₇ or KMnO₄) → ethanoic acid.

What are alcohols in Cambridge IGCSE Chemistry?

Alcohols are organic compounds with an –OH group bonded to a carbon atom. Ethanol is the most tested alcohol — used as a fuel, solvent and in alcoholic drinks. The syllabus requires you to compare fermentation and hydration as manufacturing routes, write combustion equations, and describe oxidation to carboxylic acids.

Read the full notes on Tutopiya’s Alcohols subtopic page before attempting questions.

The core ideas you must master

Process	Equation / detail	Conditions
Fermentation	C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂	Yeast, ~35 °C, anaerobic, aqueous
Hydration of ethene	C₂H₄ + H₂O → C₂H₅OH	H₃PO₄ catalyst, 300 °C, 60 atm
Combustion	C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O	Excess oxygen, heat
Oxidation to acid	C₂H₅OH → CH₃COOH	Acidified K₂Cr₂O₇ or KMnO₄, heat
Functional group	–OH (hydroxyl)	Defines alcohol homologous series

Fermentation vs hydration — comparison table

Feature	Fermentation	Hydration of ethene
Raw material	Glucose (from plants)	Ethene (from cracking)
Conditions	Yeast, ~35 °C, no oxygen	H₃PO₄, 300 °C, 60 atm
Rate	Slow, batch process	Fast, continuous process
Purity	Dilute ethanol; needs distillation	Pure ethanol directly
Sustainability	Renewable (biomass)	Uses fossil-fuel-derived ethene

Alcohols in past-paper wording: command words that matter

Command word	What the question wants	Typical alcohols stem
Describe	Process with conditions	”Describe how ethanol is made by fermentation.”
State	Product or reagent	”State the product when ethanol is oxidised.”
Compare	Two manufacturing methods	”Compare fermentation and hydration of ethene.”
Write	Balanced equation	”Write an equation for the combustion of ethanol.”
Explain	Advantage of a method	”Explain why fermentation uses anaerobic conditions.”

Worked exam-style stems (how to answer the wording)

1. “Describe how ethanol is made by fermentation.” Glucose solution is warmed with yeast at about 35 °C in the absence of oxygen. Yeast enzymes convert glucose to ethanol and carbon dioxide. Reward: glucose + yeast + temperature + anaerobic + products.
2. “Write an equation for the complete combustion of ethanol.” C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O. Reward: balanced equation.
3. “State what is formed when ethanol is oxidised with acidified potassium dichromate(VI).” Ethanoic acid (CH₃COOH). Reward: correct product name or formula.

Test yourself with the Alcohols quiz once you have worked through a few examples.

How alcohols connect to the rest of Organic Chemistry

Alcohols link to Alkenes (hydration), Carboxylic Acids (oxidation product) and Formulae, Functional Groups and Terminology. The Cambridge IGCSE Chemistry resource hub links all units.

Common mistakes students make

• Forgetting anaerobic conditions in fermentation answers.
• Confusing hydration (ethene + steam) with fermentation (glucose + yeast).
• Writing incomplete combustion products without being asked.
• Omitting acidified when naming the oxidising agent for ethanol → ethanoic acid.
• Drawing the –OH group on the wrong carbon in displayed formulae.

When you need more support

If fermentation conditions and oxidation products keep costing marks, work through the Alcohols quiz to find the gap, then get focused help from a Cambridge IGCSE Chemistry tutor.

Frequently asked questions

What is the functional group in alcohols? The hydroxyl group, –OH, bonded to a carbon atom.

How is ethanol made by fermentation? Glucose is converted to ethanol and carbon dioxide by yeast enzymes at about 35 °C in the absence of oxygen.

What is formed when ethanol is oxidised? Ethanoic acid (a carboxylic acid), using acidified potassium dichromate(VI) or potassium manganate(VII).

How do I revise alcohols effectively? Learn both manufacturing routes with conditions, practise combustion and oxidation equations, then take the Alcohols quiz.

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