Who this is for: Cambridge IGCSE Chemistry (0620) students who want carboxylic acids — ethanoic acid, reactions with metals and carbonates — to become acid-property answers instead of vague “weak acid” labels.
What query it owns: how to understand and revise carboxylic acids in Cambridge IGCSE Chemistry.
Why this is safe: this page owns the carboxylic acids revision-guide angle, while Tutopiya’s Carboxylic Acids subtopic page owns the learning resource and the free Carboxylic Acids quiz owns the practice.

Carboxylic acids contain the –COOH functional group and form the homologous series with general formula CₙH₂ₙ₊₁COOH. Cambridge IGCSE Chemistry (0620) focuses on ethanoic acid (CH₃COOH) — its formation by oxidation of ethanol, its reactions as a weak acid with metals, carbonates and alkalis, and ester formation with alcohols. This guide covers the syllabus reactions, observations and typical past-paper stems.

Key takeaways

• Carboxylic acids have general formula CₙH₂ₙ₊₁COOH; ethanoic acid is CH₃COOH.
• Ethanoic acid is a weak acid — partially ionises in water (pH ~3 for dilute solution).
• With metals (e.g. Mg): acid + metal → salt + hydrogen.
• With carbonates: acid + carbonate → salt + water + CO₂ (fizzing test for acid).
• With alcohols (conc. H₂SO₄ catalyst): acid + alcohol → ester + water.

What are carboxylic acids in Cambridge IGCSE Chemistry?

Carboxylic acids are organic acids with the –COOH group. Ethanoic acid (vinegar) is the key example. The syllabus requires you to describe reactions typical of acids, link ethanoic acid to ethanol oxidation, and know the conditions for ester formation.

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

The core ideas you must master

Reaction	Equation / observation	Key detail
Oxidation of ethanol	C₂H₅OH → CH₃COOH	Acidified K₂Cr₂O₇ or KMnO₄, heat
With magnesium	2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂	Effervescence — hydrogen gas
With sodium carbonate	2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂	Fizzing — CO₂ produced
With sodium hydroxide	CH₃COOH + NaOH → CH₃COONa + H₂O	Neutralisation
Ester formation	CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O	Conc. H₂SO₄ catalyst, heat

Carboxylic acid reactions — summary table

Reagent	Products	Observable change
Reactive metal (Mg)	Salt + H₂	Effervescence
Metal carbonate (Na₂CO₃)	Salt + H₂O + CO₂	Fizzing
Alkali (NaOH)	Salt + H₂O	Neutralisation (pH rises)
Alcohol (C₂H₅OH)	Ester + H₂O	Fruity smell (ester)

Carboxylic acids in past-paper wording: command words that matter

Command word	What the question wants	Typical carboxylic acids stem
Write	Balanced equation	”Write an equation for ethanoic acid with sodium carbonate.”
State	Product or observation	”State the gas produced when ethanoic acid reacts with a carbonate.”
Describe	Reaction with observation	”Describe the reaction between ethanoic acid and magnesium.”
Name	Ester product	”Name the ester formed from ethanoic acid and ethanol.”
Explain	Why it is a weak acid	”Explain why ethanoic acid is described as a weak acid.”

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

1. “Write an equation for the reaction between ethanoic acid and sodium carbonate.” 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂. Reward: balanced equation + CO₂.
2. “Name the ester formed from ethanoic acid and ethanol.” Ethyl ethanoate (CH₃COOC₂H₅). Reward: correct ester name.
3. “Explain why ethanoic acid is a weak acid.” It partially ionises in water — only a small fraction of molecules donate H⁺ ions, so the pH is higher than a strong acid of the same concentration. Reward: partial ionisation + comparison to strong acid.

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

How carboxylic acids connect to the rest of Organic Chemistry

Carboxylic acids link to Alcohols (oxidation source and ester partner), Formulae, Functional Groups and Terminology and Acids, Bases and Salts. The Cambridge IGCSE Chemistry resource hub links all units.

Common mistakes students make

• Calling ethanoic acid a strong acid — it is weak.
• Forgetting CO₂ as a product with carbonates.
• Naming esters incorrectly (alkyl first, then –oate: ethyl ethanoate).
• Omitting conc. H₂SO₄ as catalyst in esterification.
• Confusing oxidation of ethanol (→ acid) with fermentation (→ alcohol).

When you need more support

If acid reactions and ester naming keep costing marks, work through the Carboxylic Acids quiz to find the gap, then get focused help from a Cambridge IGCSE Chemistry tutor.

Frequently asked questions

What is the functional group in carboxylic acids? The carboxyl group, –COOH.

What gas is produced when ethanoic acid reacts with a carbonate? Carbon dioxide (CO₂) — observed as fizzing.

How is ethanoic acid formed from ethanol? By oxidation using acidified potassium dichromate(VI) or potassium manganate(VII) with heat.

How do I revise carboxylic acids effectively? Learn acid reactions with observations, practise ester naming and equations, then take the Carboxylic Acids quiz.

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