11.6Organic Chemistry

Alcohols — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 11 parts Lesson 6 of 10 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision

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Lesson summary

11.6 Alcohols — Notes — IGCSE Chemistry notes: Describe the alcohol homologous series, the manufacture of ethanol and its combustion and uses.Functional group — the hydroxyl group, –OH, is responsible for the characteristic reactions.- General formula — CnH2n+1OH, and members dif…

Renewable fuel
Energy released
Disinfectant
Other uses
Lower alcohols
Boiling point

Part 1 of 9The alcohols

The alcohols

Functional group

Functional group the hydroxyl group, –OH, is responsible for the characteristic reactions.

- General formula

CnH2n+1OH, and members differ by –CH₂–.

Name	Formula
Methanol	CH₃OH
Ethanol	C₂H₅OH (CH₃CH₂OH)
Propanol	C₃H₇OH

Naming

Naming name the alcohol from the number of carbon atoms and the –OH group.

Ethanol

Ethanol it is colourless, volatile and flammable, and it mixes with water.

It boils at 78 °C, higher than ethane, because of hydrogen bonding between its molecules.

Part 2 of 9Combustion and uses of ethanol

Combustion and uses of ethanol

Combustion

Combustion ethanol burns in excess oxygen to give carbon dioxide and water, C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.

Uses

Uses a solvent and a fuel, including as a fuel for cars.

Drinks

Drinks it is the alcohol found in wine and beer.

Renewable fuel

Renewable fuel ethanol from fermentation is a renewable biofuel.

Flame

Flame alcohols burn with a pale blue flame, so ethanol is useful in spirit burners or mixed with petrol.

Energy released

Energy released the energy released per mole increases with chain length.

Solvent

Solvent ethanol is used in perfumes, cosmetics, paints and medicines.

Disinfectant

Disinfectant ethanol and propan-2-ol kill microbes and evaporate quickly.

Other uses

Other uses methanol is a chemical feedstock and is used in antifreeze.

Safety

Safety excess ethanol damages the liver and judgement, and methanol is toxic.

Growing crops for bioethanol competes with food production.

Part 3 of 9Physical properties of alcohols

Lower alcohols

Lower alcohols methanol, ethanol and propanol are colourless liquids that mix completely with water.

Boiling point

Boiling point it rises with chain length: methanol 65 °C, ethanol 78 °C, propan-1-ol 97 °C and butan-1-ol 118 °C.
It is higher than for alkanes of similar mass because of hydrogen bonding.

Solubility

Solubility it decreases as the hydrocarbon chain gets longer.

Hazard

Hazard alcohols are flammable and volatile.

Part 4 of 9Hydration of ethene

A mixture of ethene and steam is passed over a hot catalyst of phosphoric acid.

The temperature is about 300 °C and the pressure is 60 atmospheres (6000 kPa).

The gaseous ethanol is condensed into a liquid.

4Equation

C₂H₄ + H₂O → C₂H₅OH.

5Reversible

Reversible the reaction is reversible, so unreacted ethene is recycled to increase the yield.

6Source of ethene

Source of ethene cracking of oil fractions.

Part 5 of 9Fermentation of glucose

Conditions

Conditions aqueous glucose with yeast at 25–35 °C in the absence of oxygen for a few days.

Role of yeast

Role of yeast yeast contains enzymes that catalyse the breakdown of sugar, respiring anaerobically.

Equation

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.

Temperature

Temperature too low gives a rate that is too slow and too high denatures the enzymes.

Batch process

Batch process the yeast is killed when the alcohol concentration reaches about 15%, so the vessel is emptied and the process restarted.

Dissolve sugar or starch in water and add yeast, whose enzymes break starch or sugar down to glucose.

An airlock lets the carbon dioxide escape while keeping oxygen out.

Concentration

Concentration fractional distillation of the dilute product gives a more concentrated ethanol.

Part 6 of 9Comparing the methods (Extended)

Feature	Hydration of ethene	Fermentation
Equipment	Complex	Simple
Raw materials	Non-renewable (crude oil)	Renewable (sugar cane)
Type of process	Continuous	Batch
Rate	Fast	Very slow (several days)
Quality of product	Pure ethanol	Dilute solution needing further processing
Atmospheric effects	No greenhouse gases made directly, but fossil fuels are burned for heat	Carbon dioxide is produced
Conditions	High temperature and pressure, so higher energy cost	Low temperature
Atom economy	100%, one product	Lower, because carbon dioxide is a by-product

Part 7 of 9Making ethanoic acid from ethanol

Oxidation

Oxidation ethanol can be oxidised to ethanoic acid.

Reaction with acid

Reaction with acid alcohols react with carboxylic acids to form esters.

Oxidising agents

Oxidising agents ethanol is heated with acidified potassium manganate(VII) or acidified potassium dichromate(VI) (orange to green),
- and the colour change shows oxidation has occurred.
- (purple to colourless)

Microbes in air oxidise the ethanol in wine to ethanoic acid, so wine turns to vinegar.

Part 8 of 9Other reactions of alcohols

With carboxylic acids

With carboxylic acids a concentrated sulfuric acid catalyst gives an ester and water.

With sodium

With sodium it gives hydrogen and sodium ethoxide, more slowly than water: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂.

Dehydration

Dehydration ethanol passed over hot aluminium oxide gives ethene and water.

Oxidation equation

C₂H₅OH + 2[O] → CH₃COOH + H₂O.

Part 9 of 9More from the specification

1Industrial Production Methods of Ethanol

Ethanol is synthesized either through the catalytic hydration of ethene with steam or by yeast fermentation of aqueous glucose at 30–35 °C in anaerobic conditions (batch process using renewable plant starch).
- (fast, continuous, high purity)

2Complete Combustion of Alcohols

Alcohols burn cleanly with a blue flame in oxygen to produce carbon dioxide and water: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O,
- making them viable renewable biofuels.

3Controlled Oxidation to Carboxylic Acids

Warming ethanol with acidified potassium manganate(VII) or acidified potassium dichromate(VI) oxidises the terminal hydroxyl group to form ethanoic acid (CH₃COOH).

4Covalent bond

A shared pair of electrons between two atoms, giving noble gas configurations.

5Substitution reaction

A reaction in which one atom or group is replaced by another.

6Ultraviolet radiation

Radiation that provides the activation energy for alkane–halogen reactions.

7Alkene

A hydrocarbon with a C=C bond and a name ending in -ene.

8Bromine water

An orange solution that is decolourised by alkenes.

9Addition reaction

A reaction in which atoms add across a C=C bond to give one product.

10Displayed formula

A formula showing all atoms and all bonds.

Key terms

Term	Meaning
Alcohol	Compound containing the –OH functional group.
Fermentation	Glucose to ethanol and CO₂ using yeast at 25–35 °C without oxygen.
Hydration	Addition of steam to ethene to make ethanol.
Batch process	Everything is mixed in a vessel, left, and the process repeated.
Continuous process	Reactants are constantly passed over a catalyst.
Hydroxyl group	the –OH functional group of alcohols.
Oxidising agent	a substance that supplies oxygen, shown as [O].
Hydrogen bonding	a strong attraction between molecules containing –OH groups.

Avoid these mistakes

Mixing up the conditions — hydration uses steam, 300 °C, 60 atm and an acid catalyst, and fermentation uses yeast at 25–35 °C without oxygen.

Saying fermentation needs oxygen — it is anaerobic.

Saying fermentation is continuous — it is a batch process.

Saying the –OH in alcohols makes them alkalis — alcohols are not alkaline.

Saying ethanol is oxidised to ethane — it is oxidised to ethanoic acid

Last updated: 18 October 2026