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A Level · Cambridge (CIE) · 9701

Neutralise carboxylic acids with alkalis

Neutralisation produces a carboxylate salt and water, with no gas released.

Carboxylic acids and derivatives · Cambridge 9701 AS Chemistry · 18.1

AS Level; Cambridge International Chemistry 9701, 2025–2027 syllabus. Track the carbon skeleton, name reagents and conditions, and show products and observations. Written practice is self-checked

Before you begin

  • Use alcohol oxidation and carbonyl chemistry from Topics 16–17, functional-group names, acid–base equations and balanced reaction formulae.

Work on paper. Try each question before revealing help, and explain why your method works.

Quick readiness check

What are the products of carboxylic-acid neutralisation by NaOH?

What you will learn

  • Write an acid–base equation
  • Name the carboxylate salt
  • Distinguish neutralisation from metal reactions
Products distinguish acid reactionsReactive metal→ carboxylate + H₂gas: hydrogenAlkali→ carboxylate + H₂Ono gasCarbonate→ carboxylate + H₂O + CO₂gas: carbon dioxideLiAlH₄→ primary alcoholreductionAcid + alkali gives water but no gas
Carboxylic-acid reactions: a reactive metal gives carboxylate salt and H₂; an alkali gives salt and water; a carbonate gives salt, water and CO₂; LiAlH₄ reduces the acid to a primary alcohol. Products and gases distinguish the reaction types.

Neutralisation replaces the acidic hydrogen

A carboxylic acid reacts with an alkali such as aqueous sodium hydroxide to form a carboxylate salt and water: RCOOH + NaOH → RCOONa + H₂O.

One mole of a monoprotic carboxylic acid neutralises one mole of hydroxide ions.

Compare observations

Neutralisation forms water and salt; it does not release H₂ or CO₂ gas.

Write the metal cation and carboxylate together in the salt, for example potassium propanoate, CH₃CH₂COOK.

Pause and explain

How many moles of NaOH neutralise one mole of a monoprotic carboxylic acid?

Put the idea to work

Worked example

Write the equation for propanoic acid and sodium hydroxide.

Show the worked solution
  1. Acid plus alkali forms salt and water.
  2. The salt is sodium propanoate.
  3. Check one H₂O per monoprotic acid molecule.

Answer CH₃CH₂COOH + NaOH → CH₃CH₂COONa + H₂O.

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From guided practice to a new situation

Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.

1 · Guided

Balance the equation for butanoic acid and KOH.

Give me a hint

Replace the acidic H with K and form water.

Compare my reasoning
  1. The salt is potassium butanoate.
  2. One acid molecule reacts with one OH⁻.
  3. Write one water molecule.

CH₃CH₂CH₂COOH + KOH → CH₃CH₂CH₂COOK + H₂O.

Look for these in your work

  • Correct salt
  • Correct ratio
  • Water included
2 · Independent

A student predicts bubbles when ethanoic acid is neutralised by NaOH. Evaluate this prediction.

Give me a hint

Compare neutralisation products with metal and carbonate reactions.

Compare my reasoning
  1. NaOH is an alkali.
  2. Neutralisation forms salt and water.
  3. No gas is a product in this equation.

The prediction is incorrect: sodium ethanoate and water form, with no gas expected.

Look for these in your work

  • Reaction classified
  • Products stated
  • Observation corrected
3 · Transfer

What volume-independent mole ratio relates propanoic acid to NaOH in complete neutralisation?

Give me a hint

Count transferable acid protons.

Compare my reasoning
  1. Propanoic acid is monoprotic.
  2. One acid molecule supplies one H⁺.
  3. One OH⁻ neutralises each H⁺.

1 mol propanoic acid : 1 mol NaOH.

Look for these in your work

  • Acid type identified
  • Ion ratio reasoned
  • Mole ratio correct

Common mistakes

  • Adding H₂ gas to a neutralisation equation
  • Forgetting water
  • Leaving the acidic H in the salt formula
Recall without your notes

What can you explain now?

What are the products of carboxylic-acid neutralisation by NaOH?

Compare with the explanation

Sodium carboxylate and water

The acidic proton and OH⁻ form water.

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Make it stick

How does the equation for neutralisation differ from acid reactions with metals and carbonates?

If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.

Keep learning Chemistry

Course scope and assessment

Four hundred and forty-two original lessons map the published learning outcomes across AS Chemistry Topics 1–22 and A Level Topics 23–37, with guided, independent and transfer practice and explained answers. Every numbered subject-content topic and listed outcome tag now has a mapped lesson sequence. Topic 32 maps all 12 hydroxy-compound outcome tags in 11 lessons; Topic 33 maps all 15 carboxylic-acid and derivative outcome tags in 16 lessons; Topic 34 maps all 22 nitrogen-compound outcome tags in 20 lessons; Topic 35 maps all 12 polymerisation outcome tags in 16 lessons; Topic 36 maps all four organic-synthesis outcome tags in 14 lessons; Topic 37 maps all 22 chromatography and NMR outcome tags in 18 lessons. Cambridge's 2028–2030 Version 1 syllabus states that there are no significant changes which affect teaching from the preceding edition; the routes are aligned to that edition. This is 37 of the 37 numbered subject-content topics. Full cumulative exam assessment, Paper 3 laboratory competence, Paper 5 investigation practice and human subject-teacher review remain outstanding. Written practice is self-checked and does not certify exam readiness.

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