Esterification

Esters are sweet-smelling compounds. They are used in perfumes and as flavours. The usual school example is ethanoic acid, also called acetic acid, reacting with ethanol. A few drops of concentrated sulphuric acid act as the catalyst.

The reaction can be turned back. Heat an ester with sodium hydroxide, and you get the alcohol back plus the sodium salt of the acid. This is called saponification, because it is how soap is made.

A small example

C₂H₅OH + CH₃COOH → CH₃COOC₂H₅ + H₂O. Check the balance. Ethanol has 2 C, 6 H and 1 O. Acetic acid has 2 C, 4 H and 2 O. So the left side has 4 C, 10 H and 3 O. The ester, ethyl ethanoate, has 4 C, 8 H and 2 O. Water adds 2 H and 1 O. The right side also has 4 C, 10 H and 3 O.

Where marks go

Question 26 of CBSE's 2026-27 Science sample paper asks for the reaction of X, ethanol, with acetic acid to form a sweet-smelling substance. The 2026-27 Science marking scheme gives 1 mark for the equation above, with concentrated H₂SO₄ written over the arrow.

So the marked answer is the full equation, with water as the second product and the catalyst shown. Naming "an ester" is not the same answer. See where the marks go in CBSE Science.

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Deepti Sardana

Founder Member & Academic Lead

An IIT alumna (M.Sc., M.Phil.) with over 25 years in teaching, child psychology and learning assessment. As Academic Lead at EduBrahma, she leads the method TRUtesting uses to find where and why a child loses marks.

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