Ask A Scientist Chemistry Archive

name Nan
status student
age 14

Question - I am working with Vitamin C and how to find Vitamin C by a solution. The 
solution is the cornstarch and water mix together; and add iodine (it turns purple). 
When a Vitamin C tablet is added, the solution turned clear. I would like to know that 
why and how the solution turn from purple to clear? Thank you very much!
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When iodine is added to the starch solution, the I3(-1) ion forms a complex with the starch 
that is a deep purple, as you observed. Vitamin C is a reducing agent. So it reacts with 
the iodine complex to produce I(-1) which is colorless.

Vince Calder
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