Qualitative Test for Carbohydrates

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Qualitative test for carbohydrates They are hydrates of carbons, they are organic compounds widely .distributed in plants and animals, it has a structural and metabolic rules Most important CHO is glucose, stored in plant in the form of starch, but in animals it presents in many forms such as glycogen, also in animals some .CHO can be synthesized from fat and proteins (The general formula of CHO is ( CnH2nOn :CHO are divided into three major categories Monosaccharides: are simple sugars that can't be changed into-1 simpler sugars upon hydrolysis ( reaction with HCl), e.g. glucose, .fructose, arabinose and zylose Disaccharides: are double Monosaccharides, on hydrolysis they-2 .yield to simple sugars, e.g. maltose, sucrose and lactose Polysaccharides: are complex saccharides, e.g. dextrin in plants and-3 glycogen in animals, on hydrolysis polysaccharide yield many .simple sugars :Qualitative test to detect CHO can be based on three basic properties .Reducing property of the aldehyde and ketone group-1 Hydroxyl groups can be dehydrated by strong acid and then-2 treating the result with furfuran with several reagents to form a .colored product Those which are highly pure, so a preparation of their derivatives-3 could be performed followed by detection of CHO using various .reagents :The Tests are :Molish Test-1 This is a general test for CHO, where concentrated sulphuric acid hydrolyses glycoside bonds to give monosaccharide which then dehydrated to give furfural (from pentoses) or derivative (hydroxylmethyl furural) from hexoses, which in turn combine with α-naphtol .to give purple or reddish color (Procedure: (you can see in the movie :Benedicts test-2

This test for reducing sugar, where carbohydrates with free aldehyde or ketone group have reducing propertied in alkaline solution of copper hydroxide, forming rust-brown cupperous oxides .precipitate

(Procedure: (you can see in the movie :Seliwanoffs test-3 This test is used to distinguish an aldohexose form ketohexose, heating with HCl which dehydrate hexose to hydroxymethyl furfural .((HMF Ketohexoses yield large number of HMF and at faster rate than aldohexose HMF forms red condensation product with resorcinol. The sugar use .(here is fructose ( ketohexoses) and glucose (aldohexose Ketohexose…… short time with HCl (in Seliwanoffs solution) gives hydroxymethylfurfural which is pink to orange color complex Aldohexose…… long time with HCl (in Seliwanoffs solution) gives hydroxymethylfurfural which is pink to orange color complex

.So the time is the key of differentiation