Page 29 - Phytochemistry -1 (PG404) / Clinical Pharmacy 2nd level students ( 2019 )

Clinical pharmacy PharmD program Third level Phytochemistry-1 (PG-504)

2. Acidify with 7 ml of 2N sulfuric acid and titrate back immediately the

excess of iodine (which did not reacted with the sugar) with 0.1 N sodium
thiosulfate, using starch as indicator The starch indicator should be added
only when the solution becomes straw yellow in color.

3. Carry out a blank experiment using 25 ml of water instead of sugar
solution.

4. Calculate the percentage of aldose (glucose) in the solution.

5. The difference between the volume of the thiosulfate taken in the

experiment and that of the blank represents the volume of thiosulfate
equivalent to the excess iodine (the amount of iodine added which did not
react)

Calculations

1 ml 0.1 N iodine solution is equivalent to 0.009 gm glucose (or any
aldohexose) and equivalent to 0.017 gm maltose or lactose.

(B – T) x 0.009 x 100

% of glucose =

V

B: ml of 0.1 N I 2 solution added

T: ml of 0.1 N Na 2S 2O 3 used in the titration

V: volume of sugar solution taken

1 molecule I 2 = 180 gm glucose

I = 90 gm glucose

1 ml 0.1 N lodine = 0.009 gm glucose (monosacch.)

1 ml 0.1 N lodine = 0.017 gm maltose (or lactose)

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