Use the stoichiometry of this reaction to calculate the mmol of I2 generated.

Question

A student crushed a vitamin C tablet that weighed 1.634g, and transferred 1.552g of the powder into a 100 mL volumetric flask. After diluting to the 100.00mL mark, they titrated a 20.00mL aliquot of this solution against 0.0106 M KIO3 ( the KIO2 was in the buret) with an excess HCl and KI. The initial buret reading was 0.53 mL; the final buret reading was 17.29 mL.

Answer 1

The first thing one needs to do for this question (and all the others that were posted following this) is to write a correctly balanced equation for what reaction(s) is/are taking place. In the iodometric titration of ascorbic acid, there are 2 reactions that take place and this is essential a redox reaction.

KIO₃ + 5I^- + 6H⁺ ==> 3I₂ + K⁺ + 3H₂O

I₂ + C₆H₈O₆ ==> C₆H₆O₆ + 2I^- + 2H⁺

How many mmoles I₂ generated?

volume KIO₃ used = 17.29 ml - 0.53 ml = 16.76 ml

mols KIO₃ used = 16.76 ml x 1 L / 1000 ml x 0.0106 mol / L = 1.777x10^-4 mols

mmoles KIO₃ used = 1.777x10^-4 mols x 1 mmol / 1x10^-3 mol = 0.1777 mmoles KIO₃

How many mmoles I₂ are generated?

0.1777 mmol KIO₃ x 3 mmol I₂ / mmol KIO₃ = 0.5331 mmols I₂ generated