Science Buddies: "Ask an Expert"

Hi, i'm doing a project within the group of chemistry. My question is "which fruit contains the most Vitamin C?". I am just starting my project. This is my method:

Mix 1 tablespoon of cornstarch into enough water to make a paste.
To this paste, add at exactly 250 milliliters of water and boil for five minutes. Allow to cool.
Add 10 drops of the starch solution to 75 milliliters of water by using your eyedropper.
Add enough iodine to produce a dark purple-blue color. Now your indicator solution is ready.
Put 5 milliliters of indicator solution (roughly 1 teaspoon) in a 15-milliliter test tube (one for each sample).
To the test tube, use a clean eyedropper to add 10 drops of juice from your fresh fruits. For solids, pulp them in a blender and strain the juice well. Wash and clean the eyedropper for each sample. Shake well.
Place all of your test tubes against a white background.
Line up the tubes from lightest to darkest purple. The lighter the solution, the higher the level of Vitamin C content. That’s because Vitamin causes the purple indicator solution to lose its color.

I am wondering, would it make a difference if i used 2.5% iodine solution instead of 2%? I found this project off the internet and it said to use 2% but i could only find 2.5% in the drugstore. No store has 2%. Would it make a difference?

thank you

Fifi

I believe that will not make a difference. The instructions say to add enough iodine to produce a dark purple color. You should achieve the same color as with a 2% solution by adding slightly less.

thanks chris,

i was also wondering, would it make a difference if i used concetrate juice? Because well i'm not sure if i can pulp the fruits and so i need to use concetrate juice. 100% pure. Would it make a difference? But i can't find concetrate juice of all the fruits.

These are the fruits i'm planning to use: orange, kiwi, grapefruit, pineapple, apple, strawberry.

Please help!!! I'm confused. I hope this works.!! Thanks for your help.


Fifi