Alcohols and Carboxylic Acids
Chemistry· 11.6, 11.7 (2026-2028 syllabus)· 22 min read
1. 1. Alcohols: Core Structures and Properties★★☆☆☆⏱ 6 min
Alcohol
Homologous series of organic compounds containing the covalently bonded hydroxyl (-OH) functional group attached to an unbranched alkyl chain for IGCSE 0620
Example:
Ethanol (C₂H₅OH), the second member of the series, is the alcohol found in alcoholic drinks
Only unbranched C1-C4 alcohols are tested: methanol (CH₃OH), ethanol (C₂H₅OH), propanol (C₃H₇OH), and butanol (C₄H₉OH). Short-chain alcohols are soluble in water and neutral to universal indicator.
Draw the full displayed structure of butanol, and label the functional group.
- 1
First draw the unbranched 4-carbon alkyl chain: C-C-C-C
- 2
Add hydrogen atoms to three of the carbon atoms so each has 4 covalent bonds total
- 3
Attach the -OH hydroxyl group to the terminal carbon at the end of the chain
- 4
Label the -OH group as the hydroxyl functional group
Exam tip:
Never draw branched isomers of alcohols unless explicitly asked; all exam questions for 0620 use unbranched structures for this topic.
2. 2. Core Reactions of Alcohols★★★☆☆⏱ 7 min
All Core tier learners must know two key reactions of alcohols: complete combustion, and fermentation to produce ethanol.
Complete combustion: Alcohols burn in excess oxygen to produce carbon dioxide and water, releasing large amounts of energy, making them useful as fuels.
Fermentation: Glucose from plant material is converted to ethanol and carbon dioxide by enzymes in yeast, at 30-40°C in anaerobic (no oxygen) conditions.
Write the balanced word equation for the complete combustion of methanol.
- 1
Identify the reactants: methanol and excess oxygen
- 2
Identify the products of complete combustion: carbon dioxide and water only
- 3
Write the full word equation: methanol + oxygen → carbon dioxide + water
3. 3. Carboxylic Acids: Core Structures and Reactions★★☆☆☆⏱ 5 min
Carboxylic Acid
Homologous series of organic compounds containing the carboxyl (-COOH) functional group, which gives them weak acidic properties
Example:
Ethanoic acid (CH₃COOH) is the main component of household vinegar
Unbranched C1-C4 carboxylic acids are tested: methanoic acid, ethanoic acid, propanoic acid, and butanoic acid. They turn blue litmus paper red, and show all typical acidic properties, but react more slowly than strong acids of the same concentration.
State the observations when a piece of magnesium ribbon is added to dilute ethanoic acid.
- 1
Recall that acids react with reactive metals to produce salt and hydrogen gas
- 2
First observation: Effervescence (fizzing) as hydrogen gas is released
- 3
Second observation: Magnesium ribbon dissolves to form a colourless solution of magnesium ethanoate
Exam tip:
When testing for carboxylic acids, adding a carbonate will produce carbon dioxide, which turns limewater milky: this is a common exam practical question.
4. 4. Extended Only: Additional Reactions★★★★☆Extended only⏱ 7 min
Extended tier learners must cover two additional reactions: oxidation of alcohols to carboxylic acids, and esterification.
Oxidation of alcohols: Heating an alcohol with an oxidizing agent (acidified aqueous potassium manganate(VII)) produces the corresponding carboxylic acid. The purple manganate(VII) solution turns colourless in this reaction.
Esterification: Heating a carboxylic acid with an alcohol in the presence of a concentrated sulfuric acid catalyst produces an ester and water. Esters have sweet fruity smells and are used in food flavourings and perfumes.
Write the word equation for the esterification reaction between methanol and propanoic acid.
- 1
Identify reactants: methanol, propanoic acid, with concentrated sulfuric acid catalyst
- 2
Name the ester: first part from alcohol (methyl) + second part from carboxylic acid (propanoate) = methyl propanoate
- 3
Write the full equation: methanol + propanoic acid →(conc. H₂SO₄) methyl propanoate + water
5. Common Pitfalls
Wrong move:
Writing the alcohol functional group as OH⁻ (hydroxide ion)
Why:
Alcohols contain covalently bonded -OH groups, not charged hydroxide ions found in alkalis.
Correct move:
Always write the alcohol functional group as -OH to indicate it is covalently attached to the alkyl chain.
Wrong move:
Naming esters with the carboxylic acid-derived part first
Why:
Ester naming convention requires the alkyl group from the alcohol to come first, followed by the carboxylate group from the acid.
Correct move:
For the reaction of ethanol and ethanoic acid, the product is ethyl ethanoate, not ethanyl ethanoate.
Wrong move:
Stating carboxylic acids are strong acids
Why:
Carboxylic acids only partially dissociate in water to release H+ ions, so they are weak acids.
Correct move:
Note that carboxylic acids have pH values of 3-5, and react slower than strong acids of the same concentration.
Wrong move:
Forgetting anaerobic conditions are required for fermentation
Why:
If oxygen is present during fermentation, ethanol is oxidized to ethanoic acid, reducing the yield of ethanol.
Correct move:
Always list three fermentation conditions: yeast catalyst, 30-40°C temperature, and no oxygen (anaerobic).
Wrong move:
Writing carbon monoxide as a product of complete combustion of alcohols
Why:
Complete combustion requires excess oxygen, so only carbon dioxide and water are produced. Carbon monoxide is only a product of incomplete combustion.
Correct move:
Only include CO/C as a product if the question explicitly states incomplete combustion is occurring.
6. Quick Reference Cheatsheet
Compound Type | Functional Group | Core Reactions | Extended Only Reactions |
|---|---|---|---|
Alcohol | -OH | Complete combustion, fermentation to make ethanol | Oxidation to carboxylic acid, esterification |
Carboxylic Acid | -COOH | Reacts with metals (salt + H₂), reacts with carbonates (salt + H₂O + CO₂) | Esterification with alcohol to form ester + water |
Ester | -COO- | Not tested at Core | Sweet fruity smell, used as flavourings/perfumes |
7. Frequently Asked
Do I need to know branched isomers of alcohols or carboxylic acids for 0620?
No, only unbranched C1-C4 members of both homologous series are tested for this syllabus.
Is esterification content required for Core tier learners?
No, esterification and alcohol oxidation are exclusively Extended tier outcomes, Core learners do not need to cover these.
Are carboxylic acids strong or weak acids?
Carboxylic acids are weak acids, as they only partially dissociate in water to release H+ ions.
Going deeper
- official_documentCIE IGCSE Chemistry 0620 2026-2028 Syllabus
- practice_packOrganic Chemistry Reaction Practice Pack
What's Next
Now that you have mastered alcohols and carboxylic acids, you are ready to move on to the final organic chemistry topics for CIE IGCSE 0620, including synthetic polymers and natural macromolecules. Make sure to practice writing word equations for all reactions covered, and memorise the functional group structures to avoid easy marks lost on identification questions. For Extended tier learners, focus on ester naming rules and oxidation reaction conditions, which are frequently tested in Paper 4 structured questions. Review past paper questions targeting this topic to get comfortable with exam phrasing and mark scheme expectations.