Lab: Iodometric Titration Of Vitamin C23

Iodometric Titration of Vitamin C23

Chem 341 Section 22

Sarah A Donnelly

Partner: Bethany Esterlen

Instructor: Dr. McJimpsey

T.A.: Sangeetha Mylapurapu

22 October 2015 Objective The purpose of this lab was to perform an iodometric titration of ascorbic acid. This was done by creating a known excess of I3-, reacting it with ascorbic acid then back titrating it with thiosulfate.

Background/Theory

Ascorbic acid, also known as Vitamin C, has the molecular formula C6H8O6.

It occurs naturally in citrus and a lot of vegetables. It is considered to be essential to a healthy diet. It helps keep muscles, bones, skin, and more, healthy.

Iodometric titrations are extremely important to redox titrations. This is due to the fact that iodine can react quickly, directly, and significantly with many substances, both

Then 2.0-g solid KI was added and allowed to completely dissolve. Then 50.00-mL of KIO3 was added to the flask. This brown solution was titrated with thiosulfate until the solution was a pale yellow. At this point, 2.0-mL of the starch indicator was added, creating a dark blue solution, and titrating was continued until the solution was colorless. This process was repeated for an additional two trials. To analyze the ascorbic acid, 1 Vitamin C tablet was crushed in a mortar and pestle and dissolved in 60.0-mL 0.3 M H2SO4. Once fully dissolved, 2.0-g solid KI and 50.00-mL KIO3 were added to create a brown solution. This was titrated with the standardized thiosulfate until pale brown then 2-mL of starch indicator were added to create a dark blue solution. The titration was continued until the solution was colorless. This process was repeated for two more trials. For the second trial, 51.98-mL of KIO3 was needed to turn the solution brown instead of 50-mL.

Results

For the standardization of the thiosulfate solution, the average molarity was found to be 0.68M with a standard deviation of