Vitamin C is an acid, why can a simple acid-base titration (like the ones from t

Question

Vitamin C is an acid, why can a simple acid-base titration (like the ones from the previous labs) not be used to determine the Vitamin C (Ascorbic Acid) content of food samples? The following redox reaction is the key step in determining V it. C contents. IO_3^-1 + I^-1 rightarrow I_2 This is a more complicated redox reaction and the best way to work this problem is to balance the reduction and oxidation half reactions first. After you balanced the two half reactions you may have to multiply with a factor in order to obtain the same number of electrons for the oxidation and reduction parts. In the final step combine the two half reactions and you should have a balanced redox reaction. Set up: 2 IO_3^-1 rightarrow I_2 Reduction: 2I^-1 rightarrow I_2 Oxidation: Complete Redox Reaction:

Explanation / Answer

Acid-base titration is not used for Vitamin C determination in food samples as there are additional acids in a juice, which will interfere with the result.

Reduction reaction is as follows

- 2IO3- + 12 H+ + 10 e- --> I2 + 6 H2O

Oxidation reaction is as follows

2 I- --> I2 + 2 e-

ascorbic acid + I2 --> 2 I- + dehydroascorbic acid.

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