This guide covers IGCSE Chemistry topic 14 (part 2): organic chemistry – alcohols, carboxylic acids, esters. You will revise alcohols (e.g. ethanol; -OH group; combustion; fermentation), carboxylic acids (e.g. ethanoic acid; -COOH; weak acid; reaction with alcohol), esters (formation from acid + alcohol; uses: perfumes, flavourings).

Key concepts to revise

• Alcohols – Contain -OH; e.g. methanol, ethanol; burn to CO2 + H2O; ethanol from fermentation (sugar → ethanol + CO2; yeast; anaerobic).
• Carboxylic acids – Contain -COOH; e.g. ethanoic acid; weak acids; react with alcohols to form esters (esterification); with carbonates to give CO2.
• Esters – Formed from carboxylic acid + alcohol (with concentrated H2SO4 catalyst); sweet smell; used in perfumes, flavourings.
• Fermentation – Sugar (glucose) → ethanol + CO2; yeast; anaerobic; temperature ~35–40°C; lower temperature slows; higher kills yeast.

Exam tips and command words

• State – The functional group of alcohols (-OH) and carboxylic acids (-COOH); the conditions for fermentation (yeast; anaerobic; warm).
• Write – Equation for fermentation (C6H12O6 → 2C2H5OH + 2CO2); equation for esterification (acid + alcohol → ester + water).
• Describe – How ethanol is made by fermentation (sugar; yeast; no air; warm); how an ester is made (acid + alcohol; conc H2SO4).
• Compare – Ethanol from fermentation vs from ethene + steam (fermentation: renewable; batch; ethene: from crude oil; continuous).

Common mistakes

• Writing fermentation as “glucose → ethanol” without CO2 (C6H12O6 → 2C2H5OH + 2CO2).
• Saying carboxylic acids are “strong” acids (they are weak acids; partially ionised).
• Not stating that esterification is reversible (acid + alcohol ⇌ ester + water).

Revision checklist

• State the functional group of alcohols and carboxylic acids; give one use of ethanol and one of esters.
• Write the equation for fermentation and state the conditions (yeast; anaerobic; temperature).
• Write the equation for esterification (acid + alcohol → ester + water); state the catalyst (conc H2SO4).
• Describe the reaction of a carboxylic acid with a carbonate (salt + water + CO2).

Next steps

Book a free trial with an IGCSE Chemistry tutor to practise alcohols and esters questions, or explore Tutopiya’s learning portal for more revision resources.

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