Question

3. Comparison of tested saccharides. Compound Benedict's Test (Reducing or Non Reducing) Reducing Osazones Time required for derivative formation D-Glucose D-Fructose Sucrose Reducing Non-Reducing Reducing NA Lactose Unknown 4. The unknown most closely resembles: 5. What saccharide(s) would you expect to be produced by hydrolysis of each substance? a. Starch Glucose +

Answer 1

Compound	Osazones Time required for derivative formation
D-Glucose	6 min
D-Fructose	4 min
Sucrose	No formation of derivative
Lactose	30 min

Reducing sugars give Osazone test and non-reducing sugars won't. Hence Sucrose won't form any derivatives. In Osazone test sugars react with Phenylhydrazine hydrochloride to form Osazones. Through Osazone test we can identify the sugar by the structure of crystal formed and by the time taken for the formation of crystal. The crystals will be appeared by boiling followed by slow cooling.

In Benedict's test the reducing sugar react with the Cu(II) compound to form colored compound. Here the reducing sugar reduces the Cu(II) to Cu(I) which cause the color. Hence sucrose won't form any colored product, since it is a non reducing sugar.

The time given in the table is an experimental observation.

The unknown may be a polysaccharide, since only monosaccharides and disaccharides will give the Benedict's test.