Qualitative tests reducing sugars

The majority of qualitative tests for sugars depend on the reducing characteristics of free monosaccharides. Fehling s solution, which contains cupric ions, is reduced to red CU2O by aldoses or ketoses. Similarly Tollen s test involves the reduction of Ag(NH2)2 to metallic silver. 

Oxidation with Benedict s reagent (Section 25 19) Sugars that con tain a free hemiacetal function are called reducing sugars They react with copper(ll) sulfate in a sodium citrate/sodium carbonate buffer (Benedict s reagent) to form a red precipitate of copper(l) oxide Used as a qualitative test for reducing sugars... 

Sugars may be tested for with Fehling s solution in the tannin solution treated with lead acetate and then with sodium sulphate and subsequently inverted. Since, however, tanning materials generally contain a certain quantity of reducing sugars, addition of glucose cannot always be proved by a mere qualitative test,... 

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