Carbohydrate Test

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AIM: To test the presence of carbohydrate in the given food sample.

 PROCEDURE:

S. No. Exepriment Observation Inference
1

CONC H2SOTEST

Food sample + concentrated H2SO4. Heat

Charring occurs with the smell of burnt sugar Carbohydrate present.
OR
2

MOLISCH’S TEST

Food sample + Molisch’sreagent (1% alcoholic solution of α naphthol) + concentrated H2SO4along the sides of the test tube.

 A purple ring is obtained at the junction of the two layers.  Carbohydrate present.
OR
3

BENEDICT’S / FEHLING’S TEST

Food sample + Benedict’s reagent/ Fehling’s reagent (A mixture of equal amounts of Fehling’s A and Fehling’s B). Heat.

 A red ppt. is obtained.  Carbohydrate present.
OR
4

TOLLEN’S TEST

Food sample + Tollen’s reagent (ammonium silver nitrate solution). Heat on the water bath.

 A silver mirror appears on the walls of the test tube.  Carbohydrate present.

EQUATIONS: (ON BLANK SIDE USING A PENCIL)

 1. CHO(CHOH)4CH2OH (Glucose) + 2Cu2+ + 5OH–     →  COOH(CHOH)4CH2OH(Gluconic acid)   + Cu2O + 3H2O  

2.  CHO(CHOH)4CH2OH(Glucose) + 2[Ag(NH3)2]+ + 3OH  →   COOH(CHOH)4CH2OH(Gluconic acid)  + 4NH3   + 2H2O + 2Ag                                                                                         

RESULT: : (ON RULED SIDE )  – The food sample has been tested for carbohydrate.

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