JEE Main · 2012 · 29 Apr 2012 · Offline · Biomolecules

Molisch's test is the general test for carbohydrates. A little alcoholic $\alpha$-naphthol is added to the solution and concentrated ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$ is poured gently down the side of the tube; the acid dehydrates the sugar to a furfural derivative, which condenses with $\alpha$-naphthol to give a characteristic violet ring at the junction of the two liquids. The test therefore detects sugars, and not nitro compounds, amines or simple alcohols.