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Qualitative Analysis of Carbohydrates - Benedict's Test

Qualitative Analysis of Carbohydrates in Biochemistry. <br>This test helps us to detect the presence of reducing sugar in the given sample solution when identifying a Carbohydrate.

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Qualitative Analysis of Carbohydrates - Benedict's Test

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  1. BENEDICT'S TEST To detect the presence of reducing sugar in the given solution by Benedict's Test. Dr. Almas Arshad Demonstrator, Department of Biochemistry UCMD, UOL

  2. SCHEME FOR THE DETECTION Of AN UNKNOWN CARBOHYDRATE

  3. REDUCING AND NON REDUCING SUGARS: • A sugar is a reducing sugar where the anomeric carbon has an OH group attached that can reduce other compounds. • Reducing Sugars: Glucose, Fructose, Lactose, Maltose • Non-reducing sugars: Sucrose and other polysaccharides Anomeric carbon

  4. BENEDICT'S TEST: • It is a qualitative and a semi quantitative test for simple carbohydrates. • The Benedict’s test identifies reducing sugars. • Non-reducing sugars and will not react with Benedict's solution.

  5. REAGENT: Benedict Reagent • Copper Sulphate – provides cupric ions • Sodium Citrate - complexes with the cupric ions so that they do not deteriorate to cuporousions during storage. • Sodium Carbonate - provides the alkaline conditions which are required for the redox reaction.

  6. PRINCIPLE: • On heating the mixture of reducing sugars with the Benedict's Solution, the cupric ions (Cu2+) from copper sulphate is reduced to cuprous ion (Cu1+)which is the basis of benedict’s test. • The red copper(I) oxide formed is insoluble in water and is precipitated out of solution.

  7. REACTION: Cu2++ Reducing Sugar Carboxylic Acid + Cu2O(Red precipitate)

  8. APPARATUS • Test tube • Test tube holder • Bunsen burner • Pippette • Beaker

  9. PROCEDURE: • Take 5 ml of the Benedict’s solution in a test tube with a pipette. • Add 8drops of unknown solution. • Mix thoroughly. • Boil over a flame for 2 minutes. • Cool the solution. • Observe the change in color.

  10. RESULT INTERPRETATION: • Green = 0.1 – 0.5% sugar present • Yellow = 0.5 – 1% sugar present • Orange = 1 – 1.5% sugar present • Red = 1.5 – 2% sugar present • Brick Red = > 2% sugar present • After 2%, we cannot estimate the amount of reducing sugar in the given solution, that is why this is called a semi quantitative test.

  11. OBSERVATION AND INFERENCE:

  12. USE: Benedict’s solution can be used to test for the presence of glucose in urine.

  13. PERFORMANCE(STEP – 1) Take 5 ml of the Benedicts solution in a test tube with a pipette. Add 8 drops of given sample. Mix thoroughly. Play Video

  14. PERFORMANCE (STEP – 2) Boil over a flame for 2 minutes. Change in color (Brick Red) shows the presence of >2% of reducing sugar in the given solution • Face the test tube away from yourself Play Video

  15. REVISION QUESTIONS: • Make sure at the end of the practical you should know the answers to all of these question. • Why is the Benedict’s test called a semi-quantitative test? • What is the function of Copper Sulphate, Sodium citrate and Sodium Carbonate in Benedict’s reagent? • Principle of Benedict’s test? • Clinical application of Benedict’s test? • What will be the concentration of reducing sugar, if the precipitate formed is Green, Orange or Brick red color?

  16. THANK YOU

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