What happens when Vitamin C is added to an iodine and starch solution?

It's a grade 10 high school chemistry question :)





As you may already know, an iodine and starch solution is an aqueous solution with a dark violet/black color. But when you add vitamin C to the solution, what happens? Can you provide a lengthy explanation for me? Tomorrow, I'm doing an experiment which tests the levels of vitamin C in different substances, but all I need to know for now is what will happen.

What happens when Vitamin C is added to an iodine and starch solution?
Vitamin C. reacts with iodine:





C6H8O6 + I2 ==%26gt; C6H6O6 + 2H+ + 2 I-





So you can use titration with iodine to find out the concentration of vitamin C. Since the reaction ratio is 1:1, moles vitamin = moles I2 at the endpoint, so concentrations (M) x volumes are also equal. The reasoning is a bit like in acid-base titrations, which you might have met.





The suspended starch forms a dark blue loosely held complex (almost a solid state solution) with I2, so long as there is any, so it acts as an indicator.