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Lab Activity1: Carbohydrates

Lab Activity1: Carbohydrates. IUG, Fall 2014 Dr. Tarek M Zaida. Background. A carbohydrate is an organic compound with the general formula Cm(H 2 O)n, that is, consists only of carbon, hydrogen and oxygen, with the last two in the 2:1 atom ratio.

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Lab Activity1: Carbohydrates

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  1. Lab Activity1: Carbohydrates IUG, Fall 2014 Dr. Tarek M Zaida

  2. 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.

  3. Types of Carbohydrates

  4. 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), which then condenses with the phenolic structure resulting in a red or purple-colored compound.

  5. 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.

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

  7. 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 of boiling 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.

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