Question

Give the tests for carboxylic acid group.

Hint:

Phenols are also acidic but they generally do not react with sodium bicarbonate to give effervescence. This is an excellent way to distinguish between a carboxylic acid and a phenol.

Answer 1

Concept: Carboxylic acids (-COOH) are organic compounds characterized by the presence of at least one carboxyl group. They exhibit acidic properties and can be identified in the laboratory using specific chemical tests that produce visible changes like gas evolution or color changes.
This is the most common laboratory test for carboxylic acids. When an organic compound containing a carboxyl group is added to a saturated solution of sodium bicarbonate (NaHCO₃), a brisk effervescence is observed. • Reaction: R-COOH + NaHCO₃ R-COONa + H₂O + CO₂ • Observation: Brisk effervescence due to the evolution of Carbon dioxide gas.
Carboxylic acids react with alcohols in the presence of concentrated sulphuric acid to form esters, which have a characteristic pleasant, fruity smell. • Reaction: R-COOH + R'-OH conc. H₂SO₄ R-COOR' + H₂O • Observation: A fruity odor is detected after pouring the reaction mixture into a beaker containing water.
Being acidic in nature, carboxylic acids turn blue litmus paper red. This is a simple preliminary test to confirm the acidic nature of the substance.