Neutralise carboxylic acids with alkalis
Neutralisation produces a carboxylate salt and water, with no gas released.
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
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?
Worked example
Write the equation for propanoic acid and sodium hydroxide.
Show the worked solution
- Acid plus alkali forms salt and water.
- The salt is sodium propanoate.
- Check one H₂O per monoprotic acid molecule.
Answer CH₃CH₂COOH + NaOH → CH₃CH₂COONa + H₂O.
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Test this topic →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.
Balance the equation for butanoic acid and KOH.
Give me a hint
Replace the acidic H with K and form water.
Compare my reasoning
- The salt is potassium butanoate.
- One acid molecule reacts with one OH⁻.
- Write one water molecule.
CH₃CH₂CH₂COOH + KOH → CH₃CH₂CH₂COOK + H₂O.
Look for these in your work
- Correct salt
- Correct ratio
- Water included
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
- NaOH is an alkali.
- Neutralisation forms salt and water.
- 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
What volume-independent mole ratio relates propanoic acid to NaOH in complete neutralisation?
Give me a hint
Count transferable acid protons.
Compare my reasoning
- Propanoic acid is monoprotic.
- One acid molecule supplies one H⁺.
- 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
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.