Alcohols and Carboxylic Acids

This guide covers Topic 11, Organic chemistry — subtopics 11.6 Alcohols and 11.7 Carboxylic acids — for Cambridge IGCSE Chemistry 0620 and Cambridge O Level Chemistry 5070, 2026–2028 series. It builds on Organic Chemistry: Formulae and Naming and on the ethene addition chemistry covered in Petroleum, Alkanes and Alkenes.

Where this fits in 0620/5070

Alcohols and carboxylic acids are linked by more than just both containing oxygen: ethanol can be oxidised into ethanoic acid, and ethanoic acid can react with an alcohol to form an ester — the two functional groups sit either side of a small, connected reaction network that’s a favourite source of exam questions asking you to link separate facts together.

Syllabus coverage

CAMBRIDGE IGCSE CHEMISTRY 0620

Core

• Describing the manufacture of ethanol by fermentation (aqueous glucose, 25–35°C, yeast, absence of oxygen) and by catalytic addition of steam to ethene (300°C, 6000kPa, acid catalyst) (11.6)
• Describing the combustion of ethanol (11.6)
• Stating the uses of ethanol as a solvent and as a fuel (11.6)
• Describing the reaction of ethanoic acid with metals, bases and carbonates, including the names and formulae of the salts produced (11.7)

Supplement / Extended

• Describing the advantages and disadvantages of manufacturing ethanol by fermentation vs by catalytic addition of steam to ethene (11.6)
• Describing the formation of ethanoic acid by oxidation of ethanol, both with acidified potassium manganate(VII) and by bacterial action during vinegar production (11.7)
• Describing the reaction of a carboxylic acid with an alcohol, using an acid catalyst, to form an ester (11.7)

CAMBRIDGE O LEVEL CHEMISTRY 5070

5070 has no Core/Extended split — every outcome above, Core and Supplement alike, is required for every O Level candidate. Note that 5070’s own wording is slightly broader than 0620’s here: rather than naming ethanol and ethanoic acid specifically, 5070 asks candidates to describe the combustion of alcohols and the reactions of carboxylic acids generally, with ethanol and ethanoic acid used as the standard teaching examples rather than the only examinable ones.

Manufacturing ethanol

Ethanol is made industrially by two genuinely different routes:

Fermentation — aqueous glucose is converted by yeast, at 25–35°C, in the absence of oxygen (anaerobic):

glucose --yeast--> ethanol + carbon dioxide

Catalytic addition of steam to ethene — the same hydration addition reaction from Petroleum, Alkanes and Alkenes, run industrially at 300°C and 6000kPa/60atm with an acid catalyst:

CH2=CH2 + H2O  --acid catalyst, 300°C, 6000kPa-->  CH3CH2OH

	Fermentation	Steam + ethene
Raw material	Renewable (glucose from plants)	Non-renewable (ethene from crude oil)
Rate	Slow	Fast
Purity	Produces a dilute, impure solution — needs further distillation	Produces a pure, continuous stream
Conditions	Mild (25–35°C, atmospheric pressure)	Energy-intensive (high temperature and pressure)

Neither method is simply “better” — the trade-off between renewable-but-slow and fast-but-energy-intensive is exactly what “advantages and disadvantages” questions are testing.

Ethanol’s uses follow from its properties: as a solvent (dissolves substances water can’t) and as a fuel (burns exothermically, like other organic compounds):

C2H5OH + 3O2 → 2CO2 + 3H2O

Carboxylic acids

Carboxylic acids, functional group –COOH, behave chemically like other acids (Topic 7) — reacting with metals, bases and carbonates to produce a salt:

ethanoic acid + metal      → salt + hydrogen
                              2CH3COOH + Mg → (CH3COO)2Mg + H2

ethanoic acid + base       → salt + water
                              CH3COOH + NaOH → CH3COONa + H2O

ethanoic acid + carbonate  → salt + water + carbon dioxide
                              2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2

Salts of ethanoic acid are named ethanoates — sodium ethanoate, magnesium ethanoate — following the same salt-naming logic as inorganic acids.

Making ethanoic acid from ethanol

Ethanoic acid can be made by oxidising ethanol, two ways:

• With acidified aqueous potassium manganate(VII) — a standard laboratory oxidising agent.
• By bacterial oxidation — the process behind vinegar production, where bacteria oxidise ethanol in wine or cider into ethanoic (acetic) acid naturally.

ethanol + oxygen --[O]--> ethanoic acid + water
CH3CH2OH + 2[O] → CH3COOH + H2O

Esterification

A carboxylic acid reacting with an alcohol, using an acid catalyst, produces an ester plus water:

carboxylic acid + alcohol  --acid catalyst-->  ester + water
CH3COOH + C2H5OH  -->  CH3COOC2H5 + H2O
   (ethanoic acid)  (ethanol)      (ethyl ethanoate)

Esters are named from their two “parent” components — the alcohol part becomes the -yl prefix, the acid part becomes the -oate suffix, so ethanol + ethanoic acid gives ethyl ethanoate (see Formulae and Naming for more on naming esters).

Common mistakes

• Assuming fermentation happens in the presence of oxygen. It’s specifically anaerobic — oxygen must be excluded, or the yeast respires aerobically instead and no ethanol accumulates.
• Forgetting fermentation produces a dilute mixture, not pure ethanol. The product needs further distillation to concentrate it — a key point in “advantages and disadvantages” comparisons.
• Writing the ethanol-to-ethanoic-acid oxidation as if it were combustion. Oxidation here means the ethanol gains an oxygen atom (shown as [O]) and loses hydrogen — a different transformation from burning it completely to CO₂ and water.
• Getting the ester equation the wrong way round, or naming it backwards. The alcohol supplies the “-yl” part of the name, and the acid supplies the “-oate” part — ethyl ethanoate comes from ethanol and ethanoic acid, not the reverse.
• Forgetting ethanoic acid is a weak acid (Topic 7.1) when predicting how vigorously it reacts, compared with a strong acid like hydrochloric acid.

Quick revision checklist

• Two methods of manufacturing ethanol, with conditions for each
• (0620 Extended, 5070 required) advantages and disadvantages of fermentation vs steam-addition to ethene
• Uses of ethanol, and the combustion equation
• Reactions of ethanoic acid with metals, bases and carbonates, naming the salts produced (ethanoates)
• (0620 Extended, 5070 required) two methods of oxidising ethanol to ethanoic acid
• (0620 Extended, 5070 required) esterification: reactants, catalyst, products, and naming the ester

Related resources

• Organic Chemistry: Formulae and Naming — general formulae and naming conventions for alcohols, acids and esters
• Petroleum, Alkanes and Alkenes — the ethene-hydration route to ethanol
• Acids, Bases and Salts — the acid-reaction pattern ethanoic acid follows
• Cambridge IGCSE Chemistry hub · Cambridge O Level Chemistry hub

Written against Cambridge IGCSE Chemistry 0620 and Cambridge O Level Chemistry 5070, 2026–2028 series. Always check the current syllabus for your examination year.