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Volumetric Analysis involving vitamin C

Submitted by Anonymous (not verified) on Sun, 03/02/2008 - 06:52

The amount of vitamin C in fruit juice can be determined by titration with a standard 0.0100M iodine solution.

C6H8O6 + I2 -> C6H6O6 + 2H + 2I

If the maximum concentration of vitamin C is likely to be 0.00050g/mL, describe how you would perform the analysis.
The volume of fruit juice used and the maximum titre of iodine you would expect to obtain should be mentioned.

Well, first you will need an indicator.  This is a REDOX reaction and not an acid/base titration so you will not be able to use an acid base indicator.  How could you indicate that you have reached the equivalence point?  Hint: what substance would indicate the presence of excess I2?

Since the standardized iodine solution is 20x more concentrated than the Vitamin C solution, the volume of the Vitamin C titrated should be around 20x's the volume of the Iodine titrant.  If you were using a 10 mL burette for the iodine, and wanted to add approximately 5 mL, you should should use 100 mL of the vitamin C solution.

So no exact values should be given.

Is it good just to describe the analysis without giving exact measurements as you are not able to find them from the given values....

Right, but I think they expect you to tell what you will use as a indicator for the I2.  Do a google search if necessary to find that out, it's important.