Ethanoic acid is the acid in vinegar. It behaves like any other acid with metals, bases and carbonates, only more gently, because it is weak. Oxidise ethanol and you make it; warm it with an alcohol and a drop of sulfuric acid and you get a sweet-smelling ester.
Carboxylic acids contain the –COOH functional group; ethanoic acid is CH3COOH. Ethanoic acid is a weak acid: it reacts with metals to give a salt and hydrogen, with bases to give a salt and water, and with carbonates to give a salt, water and carbon dioxide. Its salts are ethanoates. Extended: ethanoic acid is made by oxidising ethanol, either with acidified aqueous potassium manganate(VII) or by bacterial oxidation during vinegar production. A carboxylic acid reacts with an alcohol in the presence of an acid catalyst to form an ester and water: ethanoic acid + ethanol ⇌ ethyl ethanoate + water.
Compare ethanoic acid with hydrochloric acid of the same concentration in the simulator. Only a small fraction of the ethanoic acid molecules release H+ ions.
| Reacts with | Products | Example |
|---|---|---|
| reactive metal | salt + hydrogen | 2CH3COOH + Mg → (CH3COO)2Mg + H2 |
| base (alkali) | salt + water | CH3COOH + NaOH → CH3COONa + H2O |
| carbonate | salt + water + carbon dioxide | 2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2 |
Four quick checks. Each correct answer earns XP and records this skill on your profile.
What is the functional group of a carboxylic acid?
What are the products when ethanoic acid reacts with calcium carbonate?
Why is ethanoic acid described as a weak acid?
(Extended) Which two substances react to make ethyl ethanoate?
Extended. Ethanol is oxidised: the –CH2OH end becomes –COOH. Try the oxidising agent in the simulator and watch its colour.
Extended. Mix an acid and an alcohol with a catalyst in the simulator and see which atoms end up in the water.
| Alcohol | Acid | Ester (alcohol part first, then "-oate") |
|---|---|---|
| ethanol | ethanoic acid | ethyl ethanoate |
| methanol | propanoic acid | methyl propanoate |
| propanol | methanoic acid | propyl methanoate |
| butanol | ethanoic acid | butyl ethanoate |
In an ester name the alcohol part comes first (ethyl, methyl) and the acid part second (ethanoate, propanoate), even though the formula CH3COOC2H5 is written acid part first. Methanol + ethanoic acid gives methyl ethanoate, not ethyl methanoate. Ethanoic acid is weak because it is only partly dissociated, not because it is dilute: weak and dilute mean different things.
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(Extended) Which reagent oxidises ethanol to ethanoic acid in the laboratory?
(Extended) What is the name of the ester formed from methanol and propanoic acid?
Equal volumes of 0.1 mol/dm3 ethanoic acid and 0.1 mol/dm3 hydrochloric acid are added to identical pieces of magnesium. What is observed?
(Extended) What is the role of concentrated sulfuric acid in making an ester?
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