Making esters from alcohols and carboxylic acids with a sulfuric acid catalyst and identifying them by smell

The idea

A carboxylic acid and an alcohol condense with loss of water to form an ester; the catalyst speeds the equilibrium and the product is recognised by its characteristic odour and insolubility.

Safety card

What you need

• Ethanoic acid (glacial) and propanoic acid in dropper bottles; ethanol, propan-1-ol, butan-1-ol, 3-methylbutan-1-ol and benzyl alcohol in dropper bottles (about 1 mL each per group)
• Concentrated sulfuric acid in a dropper bottle (teacher-controlled, 2 or 3 drops per tube)
• Test tubes and rack, 250 mL beaker water bath at 60 to 70 degrees Celsius, 0.5 mol/L sodium carbonate solution 50 mL in a 100 mL beaker for each group
• Thermometer, timer

How to do it

1. Put ten drops of the carboxylic acid in a test tube; the teacher adds three drops of concentrated sulfuric acid.
2. Add ten drops of the alcohol, swirl, and stand the tube in the water bath for five minutes.
3. Pour the mixture into 20 mL of sodium carbonate solution, stir until fizzing stops, and smell the surface layer by wafting; record the odour and whether an oily layer separates.
4. Repeat with different acid and alcohol pairs so the class covers at least six esters; share results.
5. Name each ester, write the equation and identify the water-forming bond; explain the role of the sulfuric acid and of the carbonate wash.
6. Compare the odour of ethyl ethanoate with a labelled sample of nail-polish remover-type solvent supplied by the teacher.

What you should see

Each pair gives a distinct smell once the acid is neutralised: ethyl ethanoate (solvent, pear-drop), propyl ethanoate (pear), butyl ethanoate (banana-like), 3-methylbutyl ethanoate (strong banana or pear drops), benzyl ethanoate (jasmine or fruity), ethyl propanoate (rum-like fruit). An oily layer of ester separates from the carbonate solution (most of these esters float on it) because esters lack hydrogen-bond donors and are much less soluble than the parent acid and alcohol. The fizz on adding the mixture to carbonate is carbon dioxide from the leftover acids.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

• The sulfuric acid is one of the reactants (it is a catalyst and a dehydrating agent; it appears unchanged at the end).
• The smell comes from the alcohol (the alcohols and acids have sharp or medicinal smells; the fruity odour is the ester).
• The water formed comes from the alcohol's OH group only (it takes the OH from the acid and the H from the alcohol).

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

• Chemistry Stage 6 Syllabus (2017), NESA; the current syllabus, taught in 2026 (codes read from the syllabus document)CH12-14CH11/12-7
• Chemistry Stage 6 Syllabus (2017), NESA; the current syllabus, taught in 2026 (codes read from the syllabus document); a Working Scientifically outcome not among those the syllabus targets in Module 7, which it allows in any moduleCH11/12-3
• Chemistry 11-12 Syllabus (2025), NESA; implemented from 2028, not yet taughtCH-12-03CH-12WS-03CH-12WS-07
• Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

1. www.nsw.gov.au/education-and-training/nesa/curriculum/science/chemistry-stage-6-2017
2. www.nsw.gov.au/sites/default/files/noindex/2025-03/chemistry-stage6-syllabus-word.docx
3. curriculum.nsw.edu.au/learning-areas/science/chemistry-11-12-2025/outcomes
4. edu.rsc.org/experiments/making-esters-from-alcohols-and-acids/1743.article
5. edu.rsc.org/resources/esters-and-perfumes/1338.article