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Discuss the Fehling's test for reducing sugars.

Discuss the Fehling's test for reducing sugars.

Answers

sharon
Starch can be recognized by the deep blue colour which develops when it is in contact with
iodine solution. This is a very sensitive test. Sugar does not react with iodine, but sugar will
reduce copper (II) in Fehling's solution to red copper (I) oxide, and this is also a sensitive
test. Starch does not react with Fehling's solution. Saliva contains enzyme catalysts, which
convert starch to sugar. This experiment investigates the progress of this reaction. Put
about 10 mL of dilute starch solution into a test-tube. Add to this 1 mL of saliva and stir
this into the starch solution. Record the time of adding the saliva. At 5-minute intervals,
remove 2 or 3 drops by means of a dropper and put them on a clean white tile, taking care to
keep them from running into each other. The dropper must be washed well between each
test. Put a little iodine solution on each drop. The decreasing intensity of the blue colour
indicates that starch is being used up. Test for increasing amounts of sugar at the same
time as testing for starch. To do this, put 2 or 3 drops of the reaction mixture into a small
test-tube. Add 3 mL of Fehling's solution and warm this mixture almost to boiling point. The
test should show that the amount of sugar is increasing. The enzyme in the saliva is
therefore slowly breaking starch down into sugar, which is a smaller molecule. In a previous
experiment yeast was used to break down sugar into ethanol, which is an even smaller
molecule. Living yeast, which is a variety of fungus, produces enzymes which act as catalysts
in the conversion:
C6H12O6 -> 2C2H5OH + 2CO2
sharon kalunda answered the question on April 12, 2019 at 09:24

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