Carbohydrate Color Tests Experiment Summary
This experiment explores color tests for carbohydrates, specifically the Molisch and Anthrone tests. The Molisch test is a general test for carbohydrates using concentrated sulfuric acid, while the Anthrone test involves the formation of a blue-green complex with carbohydrates. The presence of a purple ring indicates the presence of carbohydrates. Detailed procedures and principles are provided along with images for better understanding.
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Presentation Transcript
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.
