ChemistryICSE Class 10 · Organic Chemistry

Acetic (Ethanoic) Acid: Structure, Properties and Uses (ICSE Class 10)

Updated 17 October 2026 · Fact-checked

Acetic acid (ethanoic acid), CH₃COOH, is a monocarboxylic acid with the carboxyl group -COOH. It is a colourless liquid with the smell of vinegar; pure acid solidifies into ice-like crystals on cooling and is called glacial acetic acid. It is a weak acid: it turns blue litmus red, neutralises alkalis, releases carbon dioxide from carbonates and reacts with alcohols in the presence of concentrated sulphuric acid to form esters (esterification).

Notice the carboxyl group -COOH: only the H of its -OH ionises, so acetic acid is monobasic despite having four hydrogens.

Illustration drawn for QuestionBuddy.

Understand Acetic (Ethanoic) Acid: Structure, Properties and Uses

1. Structure. Acetic acid, $C H_{3} C O O H$ , has a methyl group joined to the carboxyl group -COOH (a carbon with a double bond to one oxygen and a single bond to an -OH). Only the hydrogen of the -OH group ionises, so it is monobasic even though it has four hydrogen atoms. It is the second member of the aliphatic monocarboxylic acids (after methanoic acid).

2. Physical properties.

Colourless liquid with a sharp, vinegar-like smell and a sour taste.
Mixes with water in all proportions.
Glacial acetic acid is the pure acid, with no water. On sufficient cooling it freezes into colourless ice-like crystals, hence the name "glacial".

3. Acidic behaviour. In water it ionises only slightly, so it is a weak acid: $C H_{3} C O O H + H_{2} O ⇌ C H_{3} C O O^{-} + H_{3} O^{+}$ . It turns blue litmus red.

4. Chemical properties.

With alkalis (neutralisation): $C H_{3} C O O H + N a O H \to C H_{3} C O O N a + H_{2} O$ (sodium ethanoate, also called sodium acetate).
With carbonates and hydrogen carbonates: brisk effervescence of carbon dioxide: $2 C H_{3} C O O H + N a_{2} C O_{3} \to 2 C H_{3} C O O N a + H_{2} O + C O_{2}$ and $C H_{3} C O O H + N a H C O_{3} \to C H_{3} C O O N a + H_{2} O + C O_{2}$ .
With reactive metals such as sodium or magnesium, hydrogen is released: $2 C H_{3} C O O H + 2 N a \to 2 C H_{3} C O O N a + H_{2}$ .
With alcohols (esterification): in the presence of a few drops of concentrated sulphuric acid and heat, acetic acid combines with an alcohol to form an ester (fruity smell) and water: $C H_{3} C O O H + C_{2} H_{5} O H ⇌ C H_{3} C O O C_{2} H_{5} + H_{2} O$ (ethyl ethanoate). The reaction is reversible; concentrated sulphuric acid acts as a catalyst and removes the water.

5. Test to tell apart from ethanol. Acetic acid turns blue litmus red and releases CO₂ with sodium hydrogen carbonate; ethanol does neither. Ethanol reacts with sodium too, so use litmus.

6. Uses. Vinegar (a dilute solution used in food and pickles); as a solvent; to make esters used in perfumes and flavours; in making dyes, plastics and rayon; as a coagulant for latex; in laboratories as a reagent.

Acetic (Ethanoic) Acid: Structure, Properties and Uses: formulas and key facts

Ionisation (weak acid): $C H_{3} C O O H + H_{2} O ⇌ C H_{3} C O O^{-} + H_{3} O^{+}$
With alkali: $C H_{3} C O O H + N a O H \to C H_{3} C O O N a + H_{2} O$
With carbonate: $2 C H_{3} C O O H + N a_{2} C O_{3} \to 2 C H_{3} C O O N a + H_{2} O + C O_{2}$
With sodium: $2 C H_{3} C O O H + 2 N a \to 2 C H_{3} C O O N a + H_{2}$
Esterification: $C H_{3} C O O H + C_{2} H_{5} O H ⇌ C H_{3} C O O C_{2} H_{5} + H_{2} O$

How to solve Acetic (Ethanoic) Acid: Structure, Properties and Uses questions

For equations on acetic acid, think of it as HA, a weak acid with an -OH that can form an ester.

1With an alkali or carbonate: write the salt sodium ethanoate (CH₃COONa), plus water, plus CO₂ for a carbonate.
2With sodium or magnesium: write the salt and hydrogen.
3With an alcohol: write the ester (alcohol part + ethanoate), water, and say concentrated H₂SO₄ and heat.
4Balance the carbon and hydrogen of the CH₃ and COOH groups carefully (acetic acid has 4 H).
5For mole numericals, M of CH₃COOH = 60 g/mol; use the mole ratio then 22.4 dm³ per mole for gases.

Acetic (Ethanoic) Acid: Structure, Properties and Uses in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Why vinegar fizzes on baking soda

Suppose a student pours vinegar, a dilute solution of acetic acid, over a spoon of baking soda (sodium hydrogen carbonate) and sees vigorous fizzing.

Name the gas and write the equation.

Try it first, then show the solutionSolution

The acid reacts with the hydrogen carbonate: $C H_{3} C O O H + N a H C O_{3} \to C H_{3} C O O N a + H_{2} O + C O_{2}$ .
The gas is carbon dioxide, which turns lime water milky.

Answer: Carbon dioxide, with sodium ethanoate and water as the other products.

Memory hook: Acid + bicarbonate = fizz of CO₂.

Tricks to remember Acetic (Ethanoic) Acid: Structure, Properties and Uses

Short memory aids. Say each one aloud once, then use it on a question the same day.

Four H, one acidic
Only the H in the -COOH group ionises: acetic acid is monobasic.
Use it when: Basicity questions.
Glacial = ice-like
Pure acetic acid freezes to ice-like crystals; "glacial" means icy.
Use it when: Explaining the name.
Ester = acid + alcohol - water
In an ester, the acid and alcohol join and water is lost.
Use it when: Writing esterification equations.

Acetic (Ethanoic) Acid: Structure, Properties and Uses: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Define glacial acetic acid · 2 marks · Short answerBoard level

What is glacial acetic acid? Why is it called "glacial"?

Try it first, then show the solutionSolution

It is pure (100 per cent) acetic acid with no water.
On sufficient cooling it freezes into ice-like crystals.

Answer: The pure acid, which forms ice-like crystals when cooled.

Example 2: Reactions in a row · 2 marks · Short answerBoard level

Write the balanced equations when acetic acid reacts with (a) sodium hydroxide, (b) sodium carbonate.

Try it first, then show the solutionSolution

(a) $C H_{3} C O O H + N a O H \to C H_{3} C O O N a + H_{2} O$ .
(b) $2 C H_{3} C O O H + N a_{2} C O_{3} \to 2 C H_{3} C O O N a + H_{2} O + C O_{2}$ .

Answer: As above.

Example 3: CO₂ from acetic acid · 3 marks · Short answerHarder board level

Find the volume of carbon dioxide at S.T.P. liberated when 12 g of acetic acid reacts with excess sodium carbonate. (C = 12, H = 1, O = 16; 1 mole of gas = 22.4 dm³)

Try it first, then show the solutionSolution

Molar mass of CH₃COOH = 24 + 4 + 32 = 60 g/mol; moles = 12 / 60 = 0.2.
2CH3COOH gives 1 CO₂, so CO₂ = 0.1 mol.
Volume = 0.1 x 22.4 = 2.24 dm³.

Answer: 2.24 dm³.

Example 4: Neutralisation mass · 3 marks · Short answerHarder board level

What mass of sodium hydroxide neutralises 6.0 g of acetic acid, and what mass of sodium ethanoate is formed? (Na = 23, O = 16, H = 1, C = 12)

Try it first, then show the solutionSolution

Moles of acid = 6.0 / 60 = 0.1; ratio 1 : 1 with NaOH.
NaOH = 0.1 x 40 = 4.0 g.
CH₃COONa: M = 82 g/mol; mass = 0.1 x 82 = 8.2 g.

Answer: 4.0 g NaOH; 8.2 g sodium ethanoate.

Example 5: Esterification and conditions · 5 marks · Long answerHOTS / competency

A student warms 3.2 g of methanol (M = 32) with excess acetic acid and a few drops of concentrated sulphuric acid. (a) Write the equation and name the ester. (b) Give two observations during or after the reaction. (c) State the role of concentrated sulphuric acid. (d) Find the maximum mass of ester possible (M = 74).

Try it first, then show the solutionSolution

(a) $C H_{3} C O O H + C H_{3} O H ⇌ C H_{3} C O O C H_{3} + H_{2} O$ ; methyl ethanoate.
(b) A sweet, fruity smell appears in place of the sharp vinegar smell; the mixture is warmed throughout.
(c) Catalyst and dehydrating agent.
(d) Moles of methanol = 3.2 / 32 = 0.1 mol; maximum ester = 0.1 x 74 = 7.4 g.

Answer: (a) Methyl ethanoate (b) Fruity smell; warming (c) Catalyst and dehydrating agent (d) 7.4 g.

Where students lose marks in Acetic (Ethanoic) Acid: Structure, Properties and Uses

The slips examiners see most often, and what to write instead.

Mistake: Calling acetic acid tetrabasic
Basicity is confused with the number of hydrogen atoms.
Do this: Only the -COOH hydrogen ionises, so it is monobasic.
Usually costs: 1 mark.
Mistake: Writing the wrong ester
Ethyl ethanoate is written as CH₃COOCH₃ or C₂H₅COOCH₃.
Wrong working
CH₃COOH + C₂H₅OH -> CH₃COOCH₃
Right working
CH₃COOH + C₂H₅OH -> CH₃COOC₂H₅ + H₂O
Do this: Join the acid part to the alcohol part and add water.
Usually costs: 1 mark.
Mistake: Leaving out conditions for esterification
Concentrated sulphuric acid and heat are not stated.
Do this: Write conc. H₂SO₄ and heat above the arrow.
Usually costs: 1 mark.
Mistake: Treating glacial as a dilute solution
Candidates say glacial acetic acid is a solution in water.
Do this: It is the pure acid.
Usually costs: 1 mark.

Exam tips

Always name the salt as sodium ethanoate (or sodium acetate) in neutralisation equations.
In esterification, name the ester and mention its fruity smell.
Use litmus or sodium hydrogen carbonate to separate acetic acid from ethanol.
Quote M = 60 g/mol for numericals and use 22.4 dm³ per mole for gases.

Practice questions on Acetic (Ethanoic) Acid: Structure, Properties and Uses

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Acetic acid is:
(a) monobasic
(b) dibasic
(c) tribasic
(d) tetrabasic
Hint
Only one H ionises.
Answer
(a) monobasic.
Q2 · 1 mark · MCQBoard level
The smell of acetic acid is similar to that of:
(a) rotten eggs
(b) vinegar
(c) ammonia
(d) burning sulphur
Hint
Food preservative.
Answer
(b) vinegar.
Q3 · 2 marks · Short answerBoard level
Write the structural formula of acetic acid and name its functional group.
Hint
CH₃ joined to COOH.
Answer
CH₃-C(=O)-OH, with a methyl group joined to the carboxyl group; functional group: carboxyl, -COOH.
Q4 · 3 marks · Short answerHarder board level
Acetic acid is a weak acid. Explain this using the equation for its ionisation, and state how it differs from hydrochloric acid.
Hint
Degree of ionisation.
Answer
$C H_{3} C O O H + H_{2} O ⇌ C H_{3} C O O^{-} + H_{3} O^{+}$ shows partial ionisation, so few hydronium ions form. HCl ionises almost completely, so it is a strong acid.
Q5 · 3 marks · Short answerHarder board level
Calculate the mass of ethyl ethanoate formed if 9.2 g of ethanol (M = 46) reacts completely with excess acetic acid and the reaction goes to completion (M of ester = 88).
Hint
1 : 1 mole ratio.
Answer
Moles of ethanol = 9.2 / 46 = 0.2; ester = 0.2 x 88 = 17.6 g.
Q6 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Acetic acid has four hydrogen atoms but is a monobasic acid.
Reason (R): Only the hydrogen of the carboxyl group can ionise in water.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Basicity depends on ionisable H.
Answer
(a).
Q7 · 4 marks · Long answerHarder board level
Two colourless liquids P and Q are tested. P turns blue litmus red and liberates a gas on adding sodium hydrogen carbonate. Q does not change litmus but liberates hydrogen with sodium. (a) Identify P and Q. (b) Name the gas from P. (c) On mixing P and Q with concentrated sulphuric acid, a fruity smell results. Name the product and the reaction type.
Hint
Acid and alcohol.
Answer
(a) P: acetic acid; Q: ethanol. (b) Carbon dioxide. (c) Ethyl ethanoate; esterification.
Q8 · 4 marks · Long answerHOTS / competency
A student dilutes glacial acetic acid with water to get vinegar and finds that its pH rises. (a) Why is the pH of the diluted solution higher? (b) Write the equation for the ionisation of acetic acid in water. (c) Why is the pH of the same concentration of HCl lower than that of acetic acid?
Hint
Strong against weak acid.
Answer
(a) Dilution lowers the hydronium ion concentration. (b) $C H_{3} C O O H + H_{2} O ⇌ C H_{3} C O O^{-} + H_{3} O^{+}$ . (c) HCl is almost fully ionised, giving more H₃O⁺ than the partly ionised acetic acid.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Formula of acetic acid?Show answer
CH₃COOH.
2.Functional group present?Show answer
Carboxyl, -COOH.
3.What is glacial acetic acid?Show answer
The pure acid that forms ice-like crystals on cooling.
4.Gas with sodium carbonate?Show answer
Carbon dioxide.
5.Name the reaction of acid with alcohol.Show answer
Esterification.

Acetic (Ethanoic) Acid: Structure, Properties and Uses: frequently asked questions

Is acetic acid a strong acid?

No, it is a weak acid because it ionises only partly in water.

What is vinegar?

A dilute aqueous solution of acetic acid.

What is an ester?

A compound with a fruity smell formed when an alcohol reacts with an acid, with loss of water.

Why does acetic acid not conduct as well as hydrochloric acid at the same concentration?

It forms fewer ions because it is only partly ionised.