Plan ester formation and hydrolysis
Move between a carboxylic acid, an ester and an alcohol by choosing esterification or hydrolysis conditions.
Section 18 · Carboxylic acids and derivatives
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
Which condition is associated with esterification in this syllabus?
What you will learn
- Choose forward or reverse reaction
- Predict reactant and product names
- State catalyst or hydrolysis conditions
The two routes connect the same groups
Esterification: carboxylic acid + alcohol ⇌ ester + water, with concentrated H₂SO₄ catalyst.
Hydrolysis: ester + water → carboxylic acid + alcohol using dilute acid or alkali and heat. Acidify after alkaline hydrolysis to obtain the free acid.
Plan from the ester name
Split an ester into its alkyl part, which identifies the alcohol, and its alkanoate part, which identifies the acid.
For methyl ethanoate, the corresponding alcohol is methanol and the acid is ethanoic acid. Name hydrolysis conditions before giving work-up.
Pause and explain
What alcohol fragment is recovered from propyl methanoate?
Worked example
Plan both hydrolysis and re-formation for ethyl ethanoate.
Show the worked solution
- Its alcohol fragment is ethyl, from ethanol.
- Its acid fragment is ethanoate, from ethanoic acid.
- Use dilute acid or alkali/heat for hydrolysis; concentrated H₂SO₄ catalyses esterification.
Answer Hydrolysis gives ethanol and ethanoic acid (or ethanoate before acidification). The reverse esterification uses ethanol + ethanoic acid, concentrated H₂SO₄ catalyst, and forms ethyl ethanoate + water.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
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.
Name the acid and alcohol that hydrolyse to give butyl ethanoate.
Give me a hint
Use alkyl then alkanoate parts.
Compare my reasoning
- Butyl identifies butanol.
- Ethanoate identifies ethanoic acid.
- Esterification can re-form the ester with concentrated H₂SO₄ catalyst.
Butan-1-ol (or the corresponding butanol) and ethanoic acid; esterification uses concentrated H₂SO₄ catalyst.
Look for these in your work
- Alcohol fragment decoded
- Acid fragment decoded
- Catalyst stated
What products form when propyl methanoate is heated with dilute acid?
Give me a hint
Split at the ester link.
Compare my reasoning
- The acid part is methanoic acid.
- The alkyl part becomes propanol.
- Use dilute acid and heat.
Methanoic acid and propanol.
Look for these in your work
- Acid named
- Alcohol named
- Conditions stated
A student uses concentrated H₂SO₄ and calls the process ester hydrolysis. Correct the route.
Give me a hint
Concentrated acid is listed as the catalyst in esterification.
Compare my reasoning
- Hydrolysis uses dilute acid or alkali and heat.
- Alkaline hydrolysis needs later acidification for free acid.
- Concentrated H₂SO₄ catalyses the reverse esterification.
Use dilute acid/alkali and heat for hydrolysis; use concentrated H₂SO₄ as catalyst when making the ester from acid and alcohol.
Look for these in your work
- Conditions contrasted
- Work-up included
- Direction corrected
Common mistakes
- Switching acid and alcohol fragments
- Using concentrated acid as hydrolysis condition
- Omitting acidification after alkaline hydrolysis
What can you explain now?
Which condition is associated with esterification in this syllabus?
Compare with the explanation
Concentrated H₂SO₄ catalyst
Concentrated sulfuric acid is the esterification catalyst.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How do ester names, reaction direction and conditions identify the acid and alcohol in a route?
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.