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Benedict’s Reagent Test for Reducing Sugars

Benedict’s reagent test for reducing sugars post we briefly summarises about: principle, reagents requirements, benedict’s test for glucose procedure, result, application and limitations of benedict’s test for glucose.

Benedict’s reagent Test for Reducing Sugars

Benedict’s test for glucose is a chemical test that can be used to determine whether or not an sample contains reducing sugars. As a result, this test can identify simple carbohydrates having a free ketone or aldehyde functional group.

benedict’s test for glucose reagent (also known as Benedict’s solution) is a complicated mixture of sodium citrate, sodium carbonate, and the pentahydrate of copper (II) sulphate, which is used in the assay. When benedict’s test for glucose reagent is subjected to reducing sugars, the reactions it undergoes result in the production of a brick-red precipitate, indicating a positive Benedict’s analysis.

It should be noted that benedict’s test for glucose can also be used to determine whether or not glucose is present in a urine sample. When glucose is present in the sample, the test produces a positive result because it identifies any aldehydes and -hydroxy ketones, and glucose is an aldose whose open-chain forms an aldehyde group.

Objectives

1. To determine the presence or absence of reducing sugar in the solution.

2. To determine the glucose concentration in the solution quantitatively.

Principle

Sugars that are reduced in an alkaline environment tautomerise and create enediols. Enediols are extremely effective lowering agents. They can convert cupric ions (Cu2+) to cuprous form (Cu+), which causes the reaction mixture to change colour.

The amount of reducing sugars present determines the coloration created and the amount of precipitate formed (cuprous oxide) when the circumstances are carefully regulated.

Benedict's Reagent Test for Reducing Sugars

Benedict’s test for Glucose

Requirements

Materials

1. Test Solutions

2. Dry Test Tubes

3. Test tube stand

4. Pipettes

5. Water Bath

Reagent

1. One litre of Benedict’s Solution can be prepared from 100 g of anhydrous sodium carbonate, 173 g of sodium citrate and 17.3 g of copper (II) sulfate pentahydrate.

Procedure

1. 2 mL (10 drops) benedict’s test for glucose reagent, pipette into three clean and dry test tubes. In each test tube containing benedict’s test for glucose reagent, add approximately 1ml of each of the test solutions and water.

2. Heat the mixture directly over the flame or in the test tubes in a boiling water bath for 3-5 minutes. Look for colour changes in the solution or the production of precipitate in the test tubes.

Results

Color change from blue to brick red precipitate (glucose), Negative Benedict’s test: no change in color (sucrose) and water.

Because the intensity of the red colour and the volume of precipitate alter as the concentration of reducing sugar in the solution changes, the result can also be interpreted as:

Benedict's Reagent Test for Reducing Sugars

Benedict’s test for Glucose

Benedict's Reagent Test for Reducing Sugars

Applications

1. Benedict’s test for glucose is most commonly used to test for the presence of glucose in urine. Glucose found to be present in urine is an indication of Diabetes mellitus.

Limitations

1. The presence of ascorbic acid, homogentisic acid, and other reducing chemicals in urine, on the other hand, can cause a positive reaction.

Further Readings

Reference