Esterification: connect the acid and alcohol parts
Build an ester plus water from a carboxylic acid and alcohol using an acid catalyst, then trace the named product's connectivity.
Section 11.7 · Carboxylic acids
Extended only (Supplement) · Chemistry 0620, 2026–2028.
Before you begin
- Identify –COOH and alcohol –OH groups.
- Interpret CH₃COOCH₃ structurally and distinguish it from an ethanoate salt.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which pair supplies the required esterification reactants?
What you will learn
- Describe acid-catalysed formation of an ester from a carboxylic acid and an alcohol.
- Account for the ester linkage and the water product in representative structures and equations.
Join the correct partners
A carboxylic acid reacts with an alcohol using an acid catalyst to form an ester and water. Ethanoic acid plus methanol gives methyl ethanoate: CH₃COOH+CH₃OH⇌CH₃COOCH₃+H₂O. With ethanol instead, CH₃COOH+C₂H₅OH⇌CH₃COOC₂H₅+H₂O gives ethyl ethanoate. The equilibrium arrows describe the reversible model; the equation alone does not promise complete conversion.
The ester has the –C(=O)–O– linkage. In methyl ethanoate, the CH₃C(=O)– part comes from the ethanoic-acid framework and –O–CH₃ identifies the alcohol-derived alkyl side. In ethyl ethanoate, the oxygen links instead to CH₂CH₃. The displayed drawings show the carbonyl double bond and the single bonds to the bridging oxygen explicitly.
Name and count the whole product
The first name part identifies the alcohol-derived alkyl group: methanol gives methyl and ethanol gives ethyl. The second name part identifies the acid-derived group: ethanoic acid gives ethanoate. Thus swapping methanol for ethanol changes methyl ethanoate to ethyl ethanoate while the acid-derived name remains ethanoate. The naming section later develops the full required unbranched four-carbon range.
Count water as a second product: the acid and alcohol atom totals exceed the ester by H₂O. Methyl ethanoate totals C₃H₆O₂; ethyl ethanoate totals C₄H₈O₂. The organic ester is not the ionic salt CH₃COONa, and using a base instead of the required alcohol gives a different acid-reaction pattern. An acid catalyst speeds the reaction but is not a new part of the ester formula.
Pause and explain
What is ethanoic acid plus methanol's ester name?
Worked example
Give the product name, structure and equation for ethanoic acid plus ethanol under the stated acid-catalysed conditions.
Show the worked solution
- Ethanol supplies the ethyl name part and ethanoic acid supplies ethanoate.
- The ester structure is CH₃COOCH₂CH₃, molecular total C₄H₈O₂.
- CH₃COOH+C₂H₅OH⇌CH₃COOC₂H₅+H₂O includes water and is stated with an acid catalyst.
Answer Ethyl ethanoate CH₃COOCH₂CH₃ (C₄H₈O₂) plus water; CH₃COOH+C₂H₅OH⇌CH₃COOC₂H₅+H₂O, acid catalyst.
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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.
Build methyl ethanoate from ethanoic acid and methanol, giving its structure, second product and catalyst.
Give me a hint
Keep C(=O)–O between the acid-derived and alcohol-derived groups.
Compare my reasoning
- The acid part is CH₃C(=O)– and the alcohol-derived side is –O–CH₃.
- Combine as CH₃COOCH₃, methyl ethanoate, with water as the second product.
- CH₃COOH+CH₃OH⇌CH₃COOCH₃+H₂O is the acid-catalysed reversible model.
Methyl ethanoate CH₃COOCH₃ plus water; CH₃COOH+CH₃OH⇌CH₃COOCH₃+H₂O, acid catalyst.
Look for these in your work
- Name and ester connectivity agree.
- Water and the required catalyst are included.
Use ethanoic acid and ethanol instead. Name the ester and check every element in the ester-plus-water equation.
Give me a hint
The ethyl group contains two carbons; include the water product.
Compare my reasoning
- The product is ethyl ethanoate, CH₃COOCH₂CH₃, molecular total C₄H₈O₂.
- Reactants CH₃COOH+C₂H₅OH total C₄H₁₀O₃.
- The ester plus H₂O also totals C₄H₁₀O₃, conserving all atoms under the acid-catalysed model.
Ethyl ethanoate CH₃COOCH₂CH₃; both reactants and ester+water total C₄H₁₀O₃, acid catalyst.
Look for these in your work
- The alcohol-derived name part is correct.
- All elements balance with water included.
Compare CH₃COONa with CH₃COOCH₃. Identify salt versus ester, give the appropriate ethanoic-acid partner for each, and state the ester catalyst.
Give me a hint
A sodium ion and a covalently linked methyl group are different partners.
Compare my reasoning
- CH₃COONa is sodium ethanoate, an ionic salt; a base such as NaOH gives it with water.
- CH₃COOCH₃ is methyl ethanoate, an organic ester; methanol is the required alcohol partner.
- The ester reaction uses an acid catalyst and forms water as well.
CH₃COONa: sodium ethanoate salt from a suitable sodium base. CH₃COOCH₃: methyl ethanoate ester from methanol, using an acid catalyst and also forming water.
Look for these in your work
- Salt and ester are distinguished by their partners and bonding.
- The ester conditions and second product are correct.
Common mistakes
- Omitting the acid catalyst or the water product.
- Reversing which name part comes from the alcohol and acid.
- Drawing the ester oxygen with three bonds or omitting the carbonyl double bond.
- Confusing an organic ester with an ionic metal ethanoate salt.
What can you explain now?
What forms when a carboxylic acid reacts with an alcohol using an acid catalyst?
Compare with the explanation
An ester and water.
The ester connection retains the acid's carbonyl and links through oxygen to the alcohol-derived group.
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Make it stick
Draw methyl and ethyl ethanoate with every atom and bond, explain each name part and balance ester plus water from the stated acid/alcohol partners.
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