Testing Vitamin C With Iodine and Starch

[hanzhongxuan2]

Can someone reply to me about the science behind testing vitamin c with iodine and starch?

[Limeybean]

Hi hanzhongxuan2

It sounds like you are asking about the chemistry involved a project similar to this one from the Science Buddies website:

http://www.sciencebuddies.org/science-f ... p044.shtml

The first thing you need to learn about is a method called titration (http://chemistry.about.com/od/demonstra ... ration.htm). Titration is a way to figure out how much of a compound (in this case vitamin C) is in a solution (orange juice) by adding a different compound to it (in this case iodine). Vitamin C reacts with iodine. In fact, iodine gains an electron from vitamin C. If there is more iodine in a solution than vitamin C then eventually the vitamin C will have no more electrons to lose to the iodine. At this point iodine will start gaining electrons from the indicator starch that was added to the solution. You will know when this happened because the solution will start to change color. If you know how much iodine you added to the solution right before the color change then you can calculate out how much vitamin C was in your solution to begin with.

In this titration electron is passed from one molecule to another in what is called an oxidation/reduction (redox) reaction. For more information on redox reactions check out the following links:
http://www.shodor.org/unchem/advanced/redox/index.html
http://aids.academickids.com/encycloped ... .php/Redox

I hope that helps!

Cheers,
Emily