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Which Orange Juice has the Most Vitamin C
Posted: Sun Oct 23, 2011 8:40 am
by danmccann
My son is doing this experiment for school. I ordered all the correct materials from Home Science Tools. We have the correct Lugol's iodine, soluble starch, 250 mg. vitamin c tablets. We followed the directions for this experiment exactly. When we prepare the starch indicator solution, it kind of clumps rather than dissolves. Then I tried regular corn starch but that turns milky colored. When we titrate the vitamin c standard solution, it does not turn blue. It does not do anything. So I tried with the fresh squeezed orange juice and that did not turn the grayish brown. I have followed all directions and have all the correct materials and equipment. I don't know what else to try. Thanks for any help or advice you can give. Project is due Oct. 25, 2011.
Re: Which Orange Juice has the Most Vitamin C
Posted: Sun Oct 23, 2011 4:07 pm
by deleted-71882
Hello danmccann,
I haven't performed the experiment you are trying, but I'll comment based on my general experience.
Starch does not dissolve in water easily. If you add grocery-store corn starch to cold water and stir, you get a suspension of the starch grains in water. The grains do not dissolve. I do not know exactly what to expect with the starch supplied in your kit, but clumping in cold or merely warm water is not unexpected.
The discussion of the experiment says, "add 1 g (which is equivalent to 1/4 teaspoon) of soluble starch to 200 mL of near-boiling distilled water." If the water is not hot enough, you will get clumps. Try again with actually boiling water. Be sure you use a container that will not break when hit by the boiling water!!!
When the starch is completely dissolved, you will have a clear, colorless liquid. If you didn't get the starch completely dissolved, I think that would explain why the titration didn't work. Let's see what happens after you solve the starch problem.
Get back to us with additional questions.
Good luck.