Carbohydrate Color Tests Experiment Summary with Molisch and Anthrone Methods
This experiment demonstrates general color tests for carbohydrates using the Molisch and Anthrone methods. The Molisch test is effective for various carbohydrates, producing a purple ring upon positive reaction with concentrated sulfuric acid and -Naphthol. The presence or absence of carbohydrates can be indicated by the test results. The procedure involves mixing the test solutions in tubes and observing the interface for the purple ring characteristic of carbohydrates. A new procedure is also presented for the same purpose, emphasizing the careful addition of concentrated sulfuric acid.
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EXPERIMENT5 General Color Tests General Color Tests for Carbohydrates for Carbohydrates
An aldose differs from a ketose in that it has a carbonyl group at the end of the carbon chain instead of in the middle
GENERAL COLOR TESTS FOR CARBOHYDRATES 1/MolischTest: 2/ AnthroneTest:
1/Molisch Test: *It is a general test for carbohydrate. *It is effective for any compound which can be dehydrated to furfural or a substituted furfural (such as hydroxymethyl furfural) by concentrated sulfuric acid. *If the carbohydrate is an oligosaccharide (e.g. disaccharide, trisaccharide etc) or a polysaccharide, the hydrolysis of the carbohydrate acetal linkage occurs simultaneously with the dehydration reaction (in polysaccharide the color develops slower).
1.MolischTest PRINCIP PRINCIPL LE: E:
*The purple ring color is due to condensation products of furfural or it's derivatives with -Naphthol. Showspositivetestfor: Allcarbohydrates. Monosaccharidesgive a rapidpositivetest. Disaccharidesandpolysaccharidesreactslower. *A negative result by this reaction is a very good evidence of the absence of carbohydrates, but a positive test is indication to the probable presence of carbohydrate. *Thymol may be used as a reagent instead of -Naphthol. *Thymol is more stable than -Naphthol, and can be applied to insoluble carbohydrates like cellulose or wood.
PROCEDURE Tube1 Tube2 Tube3 0.5% starch 10 drops 0.5% sucrose 10 drops 0.5% glucose 10 drops Water 2 ml 2 ml 2 ml -Naphthol 2 drops 2 drops 2 drops Mix Con. H2SO4 3 ml 3 ml 3 ml A purple ring at the interface is indicative of acarbohydrate.
NEW PROCEDURE Tube1 2 Tube3 Tube 0.5% starch 2 ml 0.5% sucrose 2 ml 0.5% glucose 2 ml -Naphthol 2 drops 2 drops 2 drops Mix Con. H2SO4 2ml 2ml 2ml A purple ring at the interface is indicative of acarbohydrate. Incline the test tube slowly and carefully add 3ml of concentrated sulfuric acid down the side of the tube to form a layer below the sugar solution.
2/ Anthrone Test: *It is another general test for carbohydrates. *Based on similar reactions in which anthrone is used instead of - Naphthol in Molisch test to form the color product (green to blue green color). *It is very sensitive, it will give a positive reaction with filter paper (cellulose).
*It can be used for quantitative determination of glycogen and sugar of blood. *It can be used as qualitative test, since different sugars dehydrate at different rates and produce a variety of colors.
JUST FOR YOUR INFORMATION Furfural is an organic compound derived from a variety of agricultural byproducts, including corncobs, oat, wheat bran, and sawdust. The name furfural comes from the Latin word furfur, meaning bran, referring to its usualsource. It is not a carbohydrate.
PROCEDURE: Tube1 Tube2 Tube3 Tube4 Filterpaper Small piece 0.5 1drop starch % 0.5%sucrose 1drop 0.5%glucose 1drop Blank 1drop Water 1ml 1ml 1ml 1ml Anthrone reagent 3ml 3ml 3ml 3ml Heat for 3 mins in boiling water bath. Green to blue green =positive.
