Vitamin C [ Ascorbic Acid ] is a fairly strong reducing agent and it is determined by simple titration with iodine solution which oxidizes ascorbic acid to dehydroascrbic acid. The iodine is reduced to iodide.
The excess of iodine is back titrated against standard sodium thiosulphate using starch as an indicator.
I2 + 2 Na2 S2 O3 ———->Na2 S4 O6 + NaI
Oxidation of ascorbic acid with iodine is reversible but proceeds in the forward direction in acid solution.
1) Sample of vitamin C 2) Iodine solution 0.1 N 3) Sodium thiosulphate 0.1N
4) Starch solution.
Factor:- 1cc of 0.1 M Na2S2O3 == 0.0088 GM OF VIT. C
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