Experiment 10 Oxidation of Vitamin C Introduction The antioxidant properties of Vitamin C ascorbic acid were studied in this experiment as well as different properties of Vitamin C Examples of this include how Vitamin C can be iodized by iodine and how it degrades with hit due to oxidation Finally the true Vitamin C content in a Vitamin C tablet was calculated through a series of titrations and compared the the value stated on the bottle The amount of Vitamin C in the tablet was determined utilizing a titration of potassium iodate KIO3 with a mixture of potassium iodide KI hydrochloric acid HCl and the indicator 1 0 starch solution Oxidation of Vitamin C In this first part of the experiment a sample of ascorbic acid C6H8O6 is oxidized by iodine 2 I C6 H 8 O6 I 2 C 6 H 6 O6 2 H The ascorbic acid is titrated with the 0 10 M KIO3 The solution also contains HCl and KI The iodate ion then reacts with iodide I and H to produce iodine and water 3 I 2 3 H 2 O 6 H 5 I I O 3 When all the ascorbic acid has reacted with the KIO3 the concentration of I2 increases The excess I2 then reacts with I to produce I3 which signals a brownish blackish end point This is because the triiodide I3 combines with the starch to produce a dark brownish color I 3 I 2 I For the first trial the calculated mass for the ascorbic acid was 0 401 g whereas the calculated mass for the ascorbic acid in the second trial was 0 391 g The experimental mass for first trial was exactly the same was the initial mass whereas the experimental mass for the second trial was 0 010 g less than the initial mass The end point in the titration was detected when the solution began to turn a brownish color The reaction of triiodide complexing with the starch produces the color Oxidation of Ascorbic Acid The second part of the experiment deals with boiling an aqueous solution of ascorbic acid for 10 minutes The solution is then cooled to room temperature and the amount of ascorbic acid in solution is determined This is done to show the effect of an increase in temperature on the ascorbic acid For the first trial the experimental mass of the ascorbic acid was 0 386 g and for the second trial the experimental mass was also 0 386 g Comparing this is to the intial mass of 0 401 g for both trials there was a difference of 0 15 g The oxidation of Vitamin C increases with temperature and as such cooking foods will degrade the Vitamin C It does retain some of the physiological functions but once Vitamin C is oxidized it will not be as effective as an antioxidant Analysis of Vitamin C Tablets In this part of the experiment the content of Vitamin C in commercial tablets will be determined By weighing each tablet which was roughly 0 5 g you dissolve each in its own flask that contains a solution of DI water Then you add KI HCl and the starch solution to the flask and begin titrating it with the KIO3 in the burette For the first trial it was calculated to be 79 4 mass of ascorbic acid in the tablet whereas in the second trial it was calculated to be 87 5 mass of ascorbic acid in the tablet The experimental mass of the first tablet was 0 665 g whereas the experimental mass on the second tablet was 0 616 g Comparing this to the actual mass of the ascorbic acid indicated on the label of the container which was 0 500 g we find that there was a difference of 0 165 g and 0 116 g respectively Error Although the results were close enough to the initial mass of the ascorbic acid there are still various reasons for deviations in the calculations One example of this could be in titrating with the KIO3 After rinsing the burette and refilling it with KIO3 some air bubbles may have remained which could have altered the results obtained in Part Two or Three