1. PRACTICALS
CARBOHYDRATES

2. Benedict’s test
Add 8 drops of glucose solution into a test tube containing 5mL of Benedict’s solution and boil for 2 minutes over a Bunsen flame/boiling water bath.
Allow the test to cool at room temperature and observe the precipitate.

4. Identification of reducing property of sugars
Repeat the first experiment for glucose, maltose & Sucrose at the same time.
Observe the color change/precipitate & explain your observation

5. Fehling’s test
Take 1mL of Fehling’s solution into a test tube and 6 drops of glucose solution and keep it in a hot water bath for five minutes.
Observe the brick red precipitate

6. Molisch’s test Principle
All carbohydrates (monosaccharides, disaccharides and polysaccharides) give a positive reaction for Molisch test.
It is based on the dehydration of the carbohydrate by Sulphuric acid to produce an aldehyde,
Aldehyde condenses with two molecules of α-naphthol, resulting in appearance of a purple ring at the interface

7. Test
To a 2mL of glucose solution add 4 drops of 1% solution of α- naphthol in alcohol and tilt the tube carefully without mixing.
Add 2mL of concentrated sulfuric acid by pouring it down the side of the tube.

8. Barfoed’s test Principle
Reducing monosaccharides are oxidized by the copper ion in solution to form a carboxylic acid and a reddish precipitate of copper (I) oxide within three minutes.
Reducing disaccharides undergo the same reaction, but do so at a slower rate.

9. Test
Add 1mL of sugar solution to a 3mL of freshly prepared Barfoed’s reagent and mix well
Place in a boiling water bath for 1 minute
Allow to stand at room temperature for 5 minutes
Perform this test for both glucose and maltose and compare the time takes for the formation of red precipitate

11. Seliwanoff’s Test Principle
Seliwanoff’s reagent contains a non-oxidizing acid (HCl) and resorcinol.
When a ketose is reacted with this reagent, it becomes dehydrated and a cherry-red complex forms (not a precipitate).

12. Add 10 drops of seliwanoff reagent solution into a test tube containing 2 mL of Fructose solution.
Mix well and place the test tube in the boiling water bath for 10 minutes.
Observe the cherry red colour solution..

13. Test for polysaccharides
Add 1 drop of iodine solution into 1mL of starch solution.
Observe the blue-black colour solution.
Repeat the same test for glycogen and observe the colour change
Explain your observation

15. Hydrolysis of Starch/sucrose
Place 3mL of 2% starch in two test tubes and 3mL of 2% sucrose solution in two more test tubes.
To one sample each of sucrose and starch, add 20 drops Of 10% HCl.
To the other samples of sucrose and starch, add 20 drops of H2O.

16. Label the test tubes and place in a boiling water bath for 10 minutes.
Remove the test tubes from water bath and let them cool.
To the samples containing HCl add 10% NaOH (about 20 drops) until one drop of the mixture turns litmus paper blue, indicating the HCl has been neutralized.
Perform the iodine test and Benedict’s test all four samples