Science Buddies: "Ask an Expert"

My son is doing this project "What Orange Juice has the Most Vitamin C?" We bought all the correct materials from HOme Science Tools. We have the correct starch, the correct Lugol's iodine. Ihave 250 mg. vitamin c tablets. When we mix the starch, it does not really dissolve. It kind of clumps. Also, when titraing the vitamin c solution, it does hot turn blue. It juist stays clear. I tried a few times. Then I tries with fresh orange juice and it does not turn grayish brown. I also decided to try with regular corn starch but that gets milky colored. I don't know what else to do. This expermenting should have been completed by now and the project is due Tuesday, Oct. 25th. Thanks for any help you can give me. If this email is not directed to the correct person, please foward to the correct person as I have already receive one email saying to direct to someone else.

Hi,

This is a great chemistry project.

https://www.sciencebuddies.org/science- ... p044.shtml


It sounds like the starch is not dissolved; it should be clear, not milky. The directions call for dissolving ¼ tsp in 200 ml of near boiling water. If you have used hot water, and the starch is still milky, then put it in a pan on top of the stove and continue heating it while stirring until it becomes clear, just before it boils. Once the starch is dissolved then the iodine titration should work well for you son. But please do let us know if you have any further difficulties.


Donna Hardy