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.
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.
i. Copper sulphate, ii. Sodium Citrate, and iii. Sodium Carbonate. 2. Original solution (0.8.) containing a carbohydrate.
- To 5ml of Benedict’s reagent in a test tube add 8 drops of sugar 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.
Note the colour of the precipitate at the base of the test tube.
The different colour precipitate formed. Green, yellow and brick red colour is formed then reducing sugar is present.
- Blue colour = no sugar or 0 % or negative
- Green colour = 0.5% sugar or +
- Yellow colour = 1% sugar or ++
- orange colour = 1.5 % sugar or +++
- Brick Red colour = 2% sugar or ++++
- Donot heat the test tube too much. Heat it just to boil.
- Wash the apparatus before and after the experiment.
- Carefully handle all the chemicals.