vc titration
05_SSLM_p227_294
8/19/04
11:47 AM
Page 271
Name ___________________________
Chapter 23 •
Date ___________________
Functional Groups
Class __________________
SMALL-SCALE EXPERIMENT
VITAMIN C IN TABLETS
38
Small-Scale Experiment for text Section 23.3
OBJECTIVES
• Determine the vitamin C content of vitamin C tablets by iodometric titration.
• Observe the oxidation of vitamin C in aqueous solution.
INTRODUCTION
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.
PURPOSE
© Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.
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:
CH2OH
CH2OH
H
H
C
O
O
OH
HO
C 6H 8O 6
Vitamin C
(Ascorbic acid)
ϩ I2 → 2Hϩ ϩ 2IϪ ϩ
O
C
O
OH
OH
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.
IO3Ϫ ϩ 5IϪ ϩ 6Hϩ 1 3I2 ϩ 3H2O
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
8/19/04
11:47 AM
Page 271
Name ___________________________
Chapter 23 •
Date ___________________
Functional Groups
Class __________________
SMALL-SCALE EXPERIMENT
VITAMIN C IN TABLETS
38
Small-Scale Experiment for text Section 23.3
OBJECTIVES
• Determine the vitamin C content of vitamin C tablets by iodometric titration.
• Observe the oxidation of vitamin C in aqueous solution.
INTRODUCTION
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.
PURPOSE
© Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.
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:
CH2OH
CH2OH
H
H
C
O
O
OH
HO
C 6H 8O 6
Vitamin C
(Ascorbic acid)
ϩ I2 → 2Hϩ ϩ 2IϪ ϩ
O
C
O
OH
OH
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.
IO3Ϫ ϩ 5IϪ ϩ 6Hϩ 1 3I2 ϩ 3H2O
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