Determinacion yodometrica de vitamina c

13. Iodimetric Titration of Vitamin C9
Ascorbic acid (vitamin C) is a mild reducing agent that reacts rapidly with triiodide (See Section 16-7 in the textbook). In this experiment, we will generatea known excess of I3 by the reaction of iodate with iodide (Reaction 16-18), allow the reaction with ascorbic acid to proceed, and then back titrate the excess I3 with thiosulfate (Reaction 16-19 andColor Plate 11). Preparation and Standardization of Thiosulfate Solution 1. 2. Prepare starch indicator by making a paste of 5 g of soluble starch and 5 mg of HgI2 in 50 mL of water. Pour the pasteinto 500 mL of boiling water and boil until it is clear. Prepare 0.07 M Na2S2O32 by dissolving ~8.7 g of Na2S2O3.5H2O in 500 mL of freshly boiled water containing 0.05 g of Na2CO3. Store this solutionin a tightly capped amber bottle. Prepare ~0.01 M KIO3 by accurately weighing ~1g of solid reagent and dissolving it in a 500-mL volumetric flask. From the mass of KIO3 (FM 214.00), compute themolarity of the solution. Standardize the thiosulfate solution as follows: Pipet 50.00 mL of KIO3 solution into a flask. Add 2 g of solid KI and 10 mL of 0.5 M H2SO4. Immediately titrate with thiosulfateuntil the solution has lost almost all its color (pale yellow). Then add 2 mL of starch indicator and complete the titration. Repeat the titration with two additional 50.00-mL volumes of KIO3 solution.From the stoichiometries of Reactions 16-18 and 16-19, compute the average molarity of thiosulfate and the relative standard deviation.

3.

Analysis of Vitamin C Commercial vitamin C containing100 mg per tablet can be used. Perform the following analysis three times, and find the mean value (and relative standard deviation) for the number of milligrams of vitamin C per tablet. 1. 2. Dissolvetwo tablets in 60 mL of 0.3 M H2SO4, using a glass rod to help break the solid. (Some solid binding material will not dissolve.) Add 2 g of solid KI and 50.00 mL of standard KIO3. Then titrate with...