How much iodine reacts to how much vitamin C?

Question

How much iodine reacts to how much vitamin C?

Answer 1

Iodine reacts with vitamin C.  When this happens, both the iodine and vitamin C turn into different chemicals.  If a sample contains vitamin C, iodine added to the sample will react with it and no longer be iodine.  At the same time, the vitamin C that reacts with the iodine also is no longer vitamin C.  When the amount of iodine added to the sample is greater than the amount of vitamin C that was there, all the vitamin C will be destroyed and there will be some iodine left over.  So to find out how much vitamin C is in a sample, you can add small amounts of iodine, until the iodine you add no longer disappears as soon as it is added.

Example: A 250 mg Vitamin C tablet is dissolved in 100 mL of water and mixed thoroughly. A 20 mL sample of this solution is then titrated with an iodine solution. The volume of iodine solution required to cause the appearance of the blue-black color is 7.50 mL. How much Vitamin C reacts with 1.0 mL of the iodine solution?

Solution: The original Vitamin C solution contains 250 mg in 100 mL. Therefore 20 mL contains

250 mg x 20 mL/100 mL = 50 mg

These 50 mg of Vitamin C require 7.50 mL of iodine solution to react completely. The amount of Vitamin C which reacts with 1.0 mL of iodine solution is obtained by dividing 50 mg by 7.50 mL

50 mg/7.50 mL = 6.7 mg Vit. C per mL of I2 soln.

Example 2: The iodine solution in Example 1 is then used to titrate 20 mL of a fruit juice. The volume of iodine solution required to cause the appearance of the blue-black color is 2.0 mL. How many mg of Vitamin C are contained in 20 mL of juice?

Solution: From Example 1, 1.0 mL of I2 solution reacts with 6.7 mg of Vit. C. Therefore, 2.0 mL will react with

2.0 mL of iodine solution x 6.7 mg Vit. C per mL of iodine solution = 13.4 mg of Vitamin C

Therefore, 20 mL of the juice contains 13.4 mg of Vitamin C.