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Learn0620Papers 2, 4 · ExtendedOrganic chemistryAlcohols and carboxylic acids
Organic chemistry · Subtopic 4 of 5

Alcohols, Carboxylic Acids and Esters

Ethanol is made by fermentation (yeast + sugar, 25–35 °C, no air; renewable but slow and impure) or hydration of ethene (steam, 300 °C, 60 atm, phosphoric acid; fast and pure but from non-renewable oil). Ethanol burns cleanly and is a solvent and fuel. Oxidising ethanol gives ethanoic acid, a weak acid that reacts with metals, bases and carbonates. An acid + an alcohol (with conc. H2SO4\mathrm{H_2SO_4} catalyst) gives an ester, e.g. ethyl ethanoate, used in perfumes and flavourings.

Cambridge 5070 Paper 1Cambridge 5070 Paper 2Cambridge 0620 Papers 2, 4Cambridge 0620 Papers 1, 3Edexcel 4CH1 Paper 1CEdexcel 4CH1 Paper 2C≈ 45 minRevision 1 · updated 2026-10-30
Section 1 of 14

Learning objectives

  • Compare fermentation and hydration for making ethanol.
  • Describe the combustion and oxidation of ethanol.
  • Describe reactions of carboxylic acids.
  • Name esters and write esterification equations.
Pause and think

Brazil runs many of its cars on ethanol made from sugar cane, while the UK makes ethanol for industry from ethene. Why the different choices?

Section 2 of 14

Core idea

Start hereFrom grapes to vinegar

Leave grape juice with yeast and it becomes wine (ethanol). Leave the wine open to the air and bacteria turn it sour: vinegar (ethanoic acid). Two organic families, one after the other.

The big idea

Ethanol is made by fermentation or by hydrating ethene. Oxidising ethanol gives ethanoic acid. Acids and alcohols together make esters.

1. Two ways to make ethanol

Fermentation vs hydration

Renewable but slow, or fast but from oil.

2. Esters

Worked exampleMaking an ester

Ethanoic acid reacts with methanol.

Goal
Equation and ester name.
Strategy
Acid + alcohol → ester + water.
  1. CH3COOH+CH3OH⇌CH3COOCH3+H2O\mathrm{CH_3COOH+CH_3OH\rightleftharpoons CH_3COOCH_3+H_2O}
    –OH from the acid and H from the alcohol form water.
  2. methyl ethanoate\text{methyl ethanoate}
    Alcohol part (methyl) first, acid part (ethanoate) second.
AnswerMethyl ethanoate.
✓ CheckFormula C3H6O2\mathrm{C_3H_6O_2}; atoms balance ✓.
Key takeawayWeak acid Ethanoic acid partly ionises, CH3COOH⇌CH3COO−+H+\mathrm{CH_3COOH\rightleftharpoons CH_3COO^-+H^+}, so it reacts more slowly with magnesium than HCl of the same concentration.
Pause and think

Why do fermented drinks rarely exceed about 15% ethanol?

Summary

  • Fermentation vs hydration.
  • Ethanol → ethanoic acid by oxidation.
  • Acid + alcohol → ester + water.
Key words
Fermentation
Conversion of sugar to ethanol and CO₂ by yeast.
Ester
Compound formed from a carboxylic acid and an alcohol.
Hydration
Adding water (steam) to a molecule.
HistoryPasteur and yeast. In 1857 Louis Pasteur showed that fermentation is caused by living yeast cells, not a purely chemical process, laying the foundations of microbiology.
Fun factFruity chemistry. The smell of pear drops is the ester 3-methylbutyl ethanoate; pineapple is ethyl butanoate. Food scientists build artificial flavours from esters.
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