Determine which of the three sugars tested (Glucose, Fructose and Sucrose) is a reducing sugar by heating them with Benedict's solution.

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QUALITATIVE EXPERIMENT [REDUCING SUGARS]

AIM: To determine which of the three sugars tested (Glucose, Fructose and Sucrose) is a reducing sugar by heating them with Benedict’s solution.

BACKGROUND INFORMATION:

        A carbohydrate is an organic compound that is composed of atoms of Carbon, Hydrogen and Oxygen in the ratio 1:2:1. Carbohydrates used in the experiment can be divided into two groups:

  • Monosaccharides: All monosaccharides have the general formula (CH2O) n; where ‘n’ can be any number between 3 and 9. All monosaccharides also contain a carbonyl (C=O) group and at least two hydroxyl (OH) groups. The monosaccharides used in this experiment are called Hexose, which have six carbon sugars. All the hexoses have the general formula C6H12O6. They can exist as straight chains or rings. Two common hexoses are glucose and fructose (see figure below).                                                                                    

                                                                             

Hexoses are sources of energy in respiration and are the monomers, which link together to form disaccharides and polysaccharides. The properties of monosaccharides are:

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  • Small molecules
  • Low molecular mass
  • Sweet tasting
  • Crystalline
  • Readily soluble in water

  • Disaccharides: When two monosaccharide molecules undergo a condensation reaction (A reaction between two molecules which involves the formation of a bond between two subunits and a water molecule is released), a disaccharide molecule is formed and a water molecule is removed. The bond between the two monosaccharide subunits is known as a glycosidic bond.

The general formula for a disaccharide molecule is 2[(CH2O) n] – H2O. The properties of disaccharides are:

  • Small molecules
  • Low molecular mass
  • Sweet tasting
  • Crystalline
  • Soluble in ...

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