Tests for Carbohydrates - Practice Questions & MCQ

Molisch's Test
A drop of alcoholic solution of -Naphthol is added in 2ml of carbohydrate solution and 1ml of conc.H₂SO₄ is added carefully along the side of the tube. The formation of violet ring at the junction of 2-liquids shows the presence of carbohydrate. 

Molisch’s test is a general test for all carbohydrates. In this test, carbohydrates when reacted with conc. H₂SO₄ get dehydrated to form furfural and its derivatives. When monosaccharide are treated with conc. H₂SO₄ or conc. HCl, -OH group of sugar are removed in the form of water and furfural is formed from pentose sugar and hydroxymethyl furfural is formed from hexose sugar. These products react with sulphonated α- naphthol to give a purple (violet-red) coloured complex.