Alcohols and Carboxylic Acids: Revision Notes

Condensed for revision. For the full explanation, use the Alcohols and Carboxylic Acids study guide, then test yourself with the practice questions.

Tier note: items marked (0620 Extended, 5070 required) are in the Supplement column of the 0620 syllabus: 11.6 outcome 4 (advantages and disadvantages of the two methods), 11.7 outcomes 2–3 (making ethanoic acid, esters) and 11.2 outcome 4 (naming esters). Everything else is 0620 Core. 5070 has no tiers, so O Level candidates need all of it. 5070 words two points more generally: “combustion of alcohols” and “reactions of carboxylic acids”.

Syllabus: Cambridge IGCSE Chemistry 0620 and Cambridge O Level Chemistry 5070, 2026–2028, subtopics 11.6 Alcohols and 11.7 Carboxylic acids.

Making ethanol (11.6)

	Fermentation	Catalytic addition of steam to ethene
Raw material	aqueous glucose (sugar from crops)	ethene (from cracking petroleum)
Conditions	25–35 °C, yeast, absence of oxygen	300 °C, 6000 kPa / 60 atm, acid catalyst
Equation	C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂	C₂H₄ + H₂O → C₂H₅OH

Why these fermentation conditions? Yeast enzymes work best at 25–35 °C; hotter and they are denatured, colder and the reaction is too slow. Without oxygen the yeast respires anaerobically, which is what produces ethanol.

Advantages and disadvantages (0620 Extended, 5070 required)

	Fermentation	Steam + ethene
Advantages	uses a renewable raw material; low temperature, so less energy for heating	fast; continuous process; gives pure ethanol
Disadvantages	slow; batch process; gives a dilute, impure mixture that must be distilled; needs land to grow crops	uses non-renewable ethene from petroleum; high temperature and pressure need a lot of energy

Combustion and uses of ethanol

Ethanol burns in oxygen to give carbon dioxide and water:

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

Uses: as a solvent and as a fuel.

5070 note: 5070 says “combustion of alcohols”. Other alcohols also burn to carbon dioxide and water, for example propan-1-ol:

2C₃H₇OH + 9O₂ → 6CO₂ + 8H₂O

Reactions of ethanoic acid (11.7)

Ethanoic acid, CH₃COOH, has the typical reactions of an acid, and its salts are ethanoates. (0620 Extended, 5070 required) It is a weak acid: only partially dissociated in aqueous solution.

Reacts with	Products	Example
Metals	salt + hydrogen	2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂ (magnesium ethanoate)
Bases	salt + water	CH₃COOH + NaOH → CH₃COONa + H₂O (sodium ethanoate)
Carbonates	salt + water + carbon dioxide	2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂

With a metal it fizzes (hydrogen); with a carbonate it fizzes (carbon dioxide, which turns limewater milky). (0620 Extended, 5070 required) Being a weak acid, it reacts more slowly than a strong acid of the same concentration.

5070 note: 5070 says “reactions of carboxylic acids”, so learn the pattern, not just ethanoic acid. Methanoic and propanoic acids react in the same way, giving methanoates and propanoates, for example 2C₂H₅COOH + Mg → (C₂H₅COO)₂Mg + H₂ (magnesium propanoate).

Making ethanoic acid (0620 Extended, 5070 required)

Ethanol is oxidised to ethanoic acid:

• chemically, by warming with acidified aqueous potassium manganate(VII), which changes from purple to colourless;
• biologically, by bacterial oxidation during vinegar production (the ethanol in wine or cider turns sour when left open to the air).

Esters (0620 Extended, 5070 required)

A carboxylic acid reacts with an alcohol, using an acid catalyst, to form an ester and water:

ethanoic acid + ethanol ⇌ ethyl ethanoate + water
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O

Naming: the alcohol part comes first and ends in -yl; the acid part comes second and ends in -oate.

Alcohol	Acid	Ester
methanol	ethanoic acid	methyl ethanoate, CH₃COOCH₃
ethanol	methanoic acid	ethyl methanoate, HCOOC₂H₅
propan-1-ol	ethanoic acid	propyl ethanoate, CH₃COOCH₂CH₂CH₃

The syllabus limits naming to unbranched esters from alcohols and acids with up to four carbon atoms each.

Exam traps

• Fermentation needs the absence of oxygen. “Warm” alone does not earn the temperature mark: give 25–35 °C.
• The steam-and-ethene conditions are 300 °C, 6000 kPa (60 atm), acid catalyst. Do not confuse them with the Haber process conditions.
• (0620 Extended, 5070 required) In ester names, the alcohol part is written first, even though it comes second in “acid + alcohol”. Ethanoic acid + methanol gives methyl ethanoate, not ethyl methanoate.
• Salts of ethanoic acid are ethanoates. Do not write “ethanates”, and use the systematic name rather than “acetate”.
• Balance carefully: magnesium and carbonates need two ethanoic acid molecules.

Self-test

1. State the conditions for making ethanol by fermentation.
2. Write the equation for the complete combustion of ethanol.
3. State two uses of ethanol.
4. Name the salt formed when ethanoic acid reacts with sodium hydroxide, and give its formula.
5. Write the equation for ethanoic acid reacting with sodium carbonate.
6. (0620 Extended, 5070 required) Give one advantage and one disadvantage of making ethanol from ethene.
7. (0620 Extended, 5070 required) State the colour change when ethanol is oxidised with acidified potassium manganate(VII).
8. (0620 Extended, 5070 required) Name the ester formed from propanoic acid and methanol.

Answers:

1. Aqueous glucose, yeast, 25–35 °C, absence of oxygen.
2. C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.
3. As a solvent; as a fuel.
4. Sodium ethanoate, CH₃COONa.
5. 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂.
6. Advantage: fast, continuous, or gives pure ethanol. Disadvantage: ethene comes from a non-renewable resource, or the high temperature and pressure need a lot of energy.
7. Purple to colourless.
8. Methyl propanoate.

These are original notes written for revision. Check the full syllabus wording in the official 0620 syllabus and official 5070 syllabus.