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A Level · Cambridge (CIE) · 9701

Prepare carboxylic acids by ester hydrolysis

Heat an ester with dilute acid or dilute alkali; acidify after alkaline hydrolysis to release the carboxylic acid.

Carboxylic acids and derivatives · Cambridge 9701 AS Chemistry · 18.1 / 18.2

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 is the functional-group reaction when an ester forms an acid and alcohol?

What you will learn

  • Identify the ester group
  • Use dilute hydrolysis conditions and heat
  • Distinguish acid and alkaline work-up
Acid, alcohol and ester routesCarboxylic acidRCOOH+AlcoholR′OHEster + waterRCOOR′ + H₂OEsterification · concentrated H₂SO₄ catalystHydrolysis · dilute acid or alkali · heatAfter alkaline hydrolysis: acidify carboxylate to release acidAlcohol part → alkyl name · acid part → alkanoate name
Esterification and hydrolysis connect an acid, alcohol and ester. Concentrated sulfuric acid catalyses acid + alcohol ⇌ ester + water. Hydrolysis uses dilute acid or alkali and heat; alkaline hydrolysis gives carboxylate before acidification. The alcohol and acid fragments can be read from the ester name.

Hydrolysis breaks the ester link

Heat the ester with dilute acid or dilute alkali. Acid hydrolysis gives a carboxylic acid and an alcohol; alkaline hydrolysis gives a carboxylate salt and an alcohol.

Acidify the alkaline mixture to convert the carboxylate into the free carboxylic acid. State the work-up when the question asks for the acid product.

Track the two sides of the ester

The acyl side becomes the carboxylic acid or carboxylate; the alkyl side attached through oxygen becomes an alcohol.

Hydrolysis adds the elements of water across the ester bond. Do not confuse hydrolysis with esterification, which forms an ester from an acid and alcohol.

Pause and explain

What must follow alkaline ester hydrolysis to obtain the free acid?

Put the idea to work

Worked example

Describe an alkaline route from methyl propanoate to propanoic acid.

Show the worked solution
  1. Heat the ester with dilute alkali.
  2. This forms propanoate and methanol.
  3. Acidify the propanoate to obtain propanoic acid.

Answer Heat methyl propanoate with dilute alkali, then acidify: propanoate and methanol form, followed by propanoic acid after acidification.

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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

What forms when ethyl ethanoate is heated with dilute acid?

Give me a hint

Split the ester into its acid and alcohol sides.

Compare my reasoning
  1. The acyl side is ethanoate/ethanoic acid.
  2. The alkyl side is ethyl, which gives ethanol.
  3. Acid hydrolysis uses dilute acid and heat.

Ethanoic acid and ethanol.

Look for these in your work

  • Acid product correct
  • Alcohol product correct
  • Conditions stated
2 · Independent

A learner heats an ester with dilute NaOH and isolates sodium ethanoate. How can ethanoic acid be obtained?

Give me a hint

The salt is a carboxylate.

Compare my reasoning
  1. Keep the hydrolysis product in solution.
  2. Add dilute acid after heating.
  3. The acid protonates ethanoate.

Acidify the sodium ethanoate solution to obtain ethanoic acid.

Look for these in your work

  • Work-up specified
  • Carboxylate identified
  • Acid product justified
3 · Transfer

How does the reaction direction differ between hydrolysis and esterification?

Give me a hint

Compare starting functional groups and products.

Compare my reasoning
  1. Hydrolysis starts with an ester.
  2. It produces an acid and an alcohol.
  3. Esterification starts with an acid and alcohol and forms the ester.

Hydrolysis breaks an ester into acid/alcohol products; esterification combines an acid and alcohol to form an ester and water.

Look for these in your work

  • Starting groups compared
  • Products compared
  • Water role stated

Common mistakes

  • Forgetting heat
  • Calling the alkaline product a free acid before acidification
  • Confusing hydrolysis with ester formation
Recall without your notes

What can you explain now?

What is the functional-group reaction when an ester forms an acid and alcohol?

Compare with the explanation

Hydrolysis

Hydrolysis breaks the ester using water under acidic or alkaline conditions.

After trying it yourself, choose your next review. This is your self-assessment.

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Make it stick

How do conditions and work-up distinguish acid hydrolysis from alkaline ester hydrolysis?

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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