Simple test for B.Sc Botany (H) of SKBU

1. Test for Sugar
B.Sc (H) Semister I of SKBU
By Dr. Sujit Ghosh
J K College, Purulia

2. Sugar / Carbohydrate

6. Introduction :
Fehling's solution is a chemical test used to different between reducing and non-reducing
sugars. This test is based on the reaction of a functional group of sugar molecules with
Fehling's reagent.
Fehling's A: is a blue aqueous solution of copper (II) sulphate.
Fehling's B: clear and colourless solution of potassium sodium tartrate and sodium
hydroxide.
When a sugar has reducing ability, the mixture turns from deep blue colour to green colour
suspension with a red precipitate. Some sugars are capable of reducing copper II ions to
copper I ions. This reducing ability is useful in classifying sugars. When the sugar to be
tested is added to the Fehling's solution and the mixture is heated, some sugars can be
oxidized (to lose electrons) and the Fehling's mixture can obtain this electrons (reduced)
Material:
- Test tube rack - 10 ml pipet- Distilled water- 5 test tubes- 5 spatula- Lactose- Maltose-
Glucose- Sucrose- Starch- Fehling's A and B- HCl

7. Procedure:
In this experiment you will first determine with sugars give a positive
test Fehling's reagent
Take 5 test tubes and label:
1. Glucose (Monosaccharide)
2. Sucrose (disaccharide)
3. Lactose (disaccharide)
4. Maltose (disaccharide)
5. Starch (polysaccharide ) .
Put 2 mL of distilled water inside each tube. With different spatulas
put a small amount of each sugar. Dissolve the sugar.
Add 2mL of Fehling's A solution and then Fehling's B.
Place each test-tuve in a boiling water bath (250mLbeaker on a
hotplate stirrer). Observe the happening.

8. Starch Hydrolysis:
Hydrolysis is the response of a compound with water. As you
probably are aware, starch being a polymer, comprising of
numerous units of α-D-glucose covalently connected . For starch
following schedule are following:-
Place 2mL of 1% starch in a test tube and add 0.5mL of 3M HCl.
Mix and place this mixture in a boiling water bath for 10 minutes.
After 10 minutes, remove the tube from the water bath and let it
cool. Neutralize this solution with 1M NaOH and mix well.
Transfer 8-10 drops of this solution to a small test tuve.
Add 1mL of Fehling's A solution and 1mL of Fehling's B.
Heat for a few minutes in a boiling water bath.
Compare the results of this test with your results for unhydrolyzed
starch in the step 1 of this experiment.
You can test the absence of starch with iodine solution too.