H2SO4 acts as dehydrating agent forming furfural derivatives which interact with alpha-naphthol librating a violet layered compound
Test | Molisch test | Objective | A general test for all carbohydrates. Monosaccharides give a rapid positive test. Disaccharides and polysaccharides react slower. | Principle involved | Dehydration of the carbohydrate by concentrated sulfuric acid to produce an aldehyde | Reagent | H2SO4 | Positive results | a purple-black layer/violet ring in the compound | Compound responsible | | | | Amylose in starch is responsible for the formation of a deep blue color in the presence of iodine.
The term carbohydrate originally referred to hydrates of carbon because the general formula of these compounds was CnH2Non or Cn(H2O)n.
SAMPLES | OBSERVATIONS | Glucose | There is a purple-black layer/violet ring in the compound. | Carrageenan | There is a purple-black layer/violet ring in the compound. | Chicken Liver Extract | There is a purple-black layer/violet ring in the compound. |
SAMPLES | OBSERVATIONS | | Before Heating | After Heating | On Cooling | Potato Starch | Dark Blue | Colorless | Dark blue | Carrageenan | Pale brown | Colorless | Pale brown | Chicken Liver Extract | Reddish brown | Reddish brown | Reddish brown |
POLYSACCHARIDE | COLOR With Iodine Solution | Amylose | Dark Blue (Blue-black) | Amylopectin | No color with Iodine | Glycogen | Mahogany red | Agar-agar | Violet | Carrageenan | Brown | Cellulose | No color with Iodine; Blue (after acid hydrolysis) | Dextrines: | Amylodextrine | Bluish-red (sometimes seen as violet) | | Erythrodextrine | Red | | Achrodextrine | No color with Iodine |
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