Fehling Test: A test for aldehyde and alpha hydroxy ketone скачать в хорошем качестве

Fehling Test: A test for aldehyde and alpha hydroxy ketone

#fehlingtest #fehlingtestforreducingsugar Fehling’s test is one of the sensitive test for detection of reducing sugars. Fehling’s reagents comprises of two solution Fehling’s solution A and solution B. Fehling’s solution A is aqueous copper sulphate and Fehling’s solution B is alkaline sodium potassium tartarate ( Rochelle salt). Rochelle salts (sodium potassium tartarate) present in the reagent acts as the chelating agent in this reaction.These two solution are mixed in equal amount before test. On heating an aldehyde or reducing sugar with Fehling’s solution give reddish brown prepitate. Formation of red precipitate of cuprous oxide denotes the presence of reducing sugar. Requirements for the test Test sample Dry test tubes Pipettes Water bath or burner Fehling’s reagent Fehling’s reagent: Fehling’s Solution A: Copper sulphate : 34.65 gm Final volume : 500 ml Fehling’s Solution B: Potassium hydroxide : 125 gm Rochelle salt : 173 gm (Sodium potassium tartarate) Final volume : 500 ml Mix both in equal volume Significance of Components Copper sulphate: Furnishes cupric ions (Cu++) in solution. Potassium hydroxide: Makes medium alkaline. Rochelle Salt: Prevents the precipitation of cupric ions as cupric hydroxide [Cu(OH)2] by forming a loosely bound cupric-sodium citrate complex. Principle Carbohydrates with free aldehyde or alpha hydroxy ketone groups have the ability to reduce metallic ions. They reduce cupric ions to cuprous form and are themselves converted to corresponding sugar acids. The cuprous ions combine with OH- ions to form yellow cuprous hydroxide which upon heating is converted to red cuprous oxide. Point to Note Reagent is unstable, so prepared separately and kept separately Strong alkali (potassium hydroxide) present in the reagent which can destroy carbohydrates Auto reduction may occur which gives false positive result