Benedict’s test for reducing sugar

Benedict’s test for reducing sugar:

Benedict’s test for reducing sugar is a particular test for reducing substances.This test can be: used as a rough quantitative test for the clinical evaluation.

PRINCIPLE:

In the presence of reducing sugar, cuso4 gives cupric ion in an alkaline medium which is reduced to cuprous ion cu+2 to form cuprous oxide cuo2, and different coloured precipitates are formed. Sodium citrate maintains cupric ion in the solution and prevents black discolouration of cuprous oxide.   

REAGENTS:

i. Copper sulphate, ii. Sodium Citrate, and iii. Sodium Carbonate. 2. Original solution (0.8.) containing a carbohydrate.

PROCEDURE:

• 1. To 5ml of Benedict’s reagent in a test tube add 8 drops of sugar solution

  (original solution).

• Mix thoroughly and heat to boil for 2 minutes.
• Allow the tube to cool. The solution, in addition to the formation of a precipitate, will change colour from blue to green. Yellow, orange or red depending upon the amount of reducing sugar present.

INDICATION:

Note the colour of the precipitate at the base of the test tube.

RESULT:

The different colour precipitate formed. Green, yellow and brick red colour is formed then reducing sugar is present.

Observation:

1. Blue colour = no sugar or 0 % or negative
2. Green colour = 0.5% sugar or +
3. Yellow colour = 1% sugar or ++
4. orange colour = 1.5 % sugar or +++
5. Brick Red colour = 2% sugar or ++++

NOTE:

• Donot heat the test tube too much. Heat it just to boil.

Precautions:

• Wash the apparatus before and after the experiment.
• Carefully handle all the chemicals.