Science Buddies: "Ask an Expert"

Hi,

I'm doing a Science Fair Project about how cooking fruits and vegetables lowers Vitamin C content. So basically I use boiled cornstarch+water and SIS and then I put in a few drops of raw vegetable/fruit juice or cooked vegetable/fruit juice. The color of the starch-SIS solution is usually a really dark blue, and when it comes in contact with Vitamin C, it should get a lot lighter. The idea was that the raw juice should cause the solution to have a lighter color because it has more Vitamin C and the cooked juice shouldn't really change the color that much. However, after doing several trials with different fruits and vegetables, the cooked juice always makes the starch-SIS solution lighter than the non-cooked one. I'm honestly really freaking out and running out of time and I have no clue what to do. I don't even know why the experiment is going wrong!!! Please help before May 10th, 2013.

Hello ishetak97,

I am puzzled by your result as you are. Here's one idea that may help you.

The usual way to use iodine to measure vitamin C is not to mix the iodine and starch solution first, then add vitamin C. Try this procedure.

Mix the starch solution with the fruit juice.

Then add the iodine solution slowly while stirring. Continue to add iodine solution as long as the solution remains relatively colorless.

When the solution begins to turn dark, that indicates that you have combined iodine with all the vitamin C, and the added iodine is reacting with the starch.

Good luck, WW

I need other analytical agents such as Iodine and Starch.

I need help investigating the use of sodium hydroxide as reagent to analyze vitamin C. It should be possibly to carry out an acid/base type titration because vitamin C is an acid.