Name ___________________________ Chapter 23 • Functional Groups
VITAMIN C IN TABLETS
Small-Scale Experiment for text Section 23.3
• Determine the vitamin C content of vitamin C tablets by iodometric titration. • Observe the oxidation of vitamin C in aqueous solution.
Vitamins regulate biochemical reactions that take place within living cells. The human body requires vitamins only in tiny amounts. For a compound to be classified as a vitamin, its absence in the diet must cause a specific disease that is cured when the vitamin is resupplied. Vitamin C deficiency, for example, causes scurvy, a disease common to sailors until the latter part of the eighteenth century.
In this experiment, you will use an iodometric titration to measure the amount of vitamin C in vitamin supplements. This method takes advantage of the fact that vitamin C is a water-soluble organic compound that is easily oxidized and is therefore a good reducing agent. Iodine oxidizes vitamin C according to the following equation: © Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved. CH2OH H C OH HO C 6H 8O 6 Vitamin C (Ascorbic acid) OH O O I2 → 2H 2I C OH O CH2OH H O O
C 6H 6O 6 Oxidized form of vitamin C (Dehydroascorbic acid)
Because aqueous iodine solutions are unstable and inconvenient to work with, you will titrate vitamin C samples in this lab with potassium iodate, KIO3, in the presence of an acidic iodide solution. The iodate ion oxidizes iodide to iodine. IO3 5I 6H
Notice that an equilibrium is established. To ensure that the reaction goes to completion, it is necessary to use excess iodide and to make the solution acidic. The iodine formed in this reaction immediately oxidizes the vitamin C according to the previous equation. Once all the vitamin C is oxidized, there will be an excess of I2 that...