Lab Activity1: Carbohydrates IUG, 2016 Dr. Tarek M Zaida

Background A carbohydrate is an organic compound with the general formula Cm(H2O)n, that is, consists only of carbon, hydrogen and oxygen, with the last two in the 2:1 atom ratio. Carbohydrates make up the bulk of organic substances on earth and perform numerous roles in living systems. The carbohydrates (saccharides) are divided into three categories: Monosaccharides, disaccharides, and polysaccharides.

Types of Carbohydrates Monosaccharides Found in fruits and dairy products Easily digested by the body Disaccharides Found in fruits Composed of two simple sugars Polysaccharides Commonly found in vegetables (cellulose), whole grain breads It takes longer for the body to digest

1) Molisch’s Test Molisch’s Test is a sensitive chemical test for all carbohydrates based on the dehydration of the carbohydrate by H2SO4 to produce an aldehyde (either furfural or a derivative). The resulted furfural or its derivative then condenses with the phenolic structure (α-naphthol), resulting in a red or purple-colored compound. α-naphthol

PROCEDURE Place 2 mL of a known carbohydrate solution in a test tube, add 1 drop of Molisch’s reagent (10% α-naphthol in ethanol). Pour 1-2 mL of conc. H2SO4 down the side of the test tube, so that it forms a layer at the bottom of the tube. Observe the color at the interface between two layers and compare your result with a control test.

2) Anthrone Test As in Molisch’s reaction, except for using the anthrone reagent (0.2% in conc. H2SO4), instead of α-naphthol reagent. Anthrone

Procedure 1. To 5 drops of the carbohydrates solution in a test tube carefully add 2 ml of anthrone reagent, mix thoroughly by swirling, 2. Heat in a boiling water-bath for 3 min. 3. Cool the samples and observe the color formed. The mixture should be of a greenish or blue-green color of an intensity depending on the amount of carbohydrate present.