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.
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.|
| 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|
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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