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Reaction of Iodine #10

Reaction of Iodine #10 - when it turned clear 2 In the...

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Verina Atalla November 10, 2009 Renu Jain Chem 1111C Lab The reaction of iodine with thiosulfate 1) What is the purpose of adding starch to this solution? Iodine solution is used to test for starch; a darkblue color indicates the presence of  starch. The iodine (I 3 −  and I 5 −  ions) fits inside the coils of amylose, the charge transfers  between the iodine and the starch, and the energy level spacings in the resulting  complex correspond to the absorption spectrum in the visible light region. The strength  of the resulting blue color depends on the amount of amylose present. Waxy starches  with little or no amylose present will color red. ( http://en.wikipedia.org/wiki/Starch ) In this experiment, it was important to add the starch so that we can see the reaction’s  final endpoint.  It turned the solution into a dark blue and then we titrated it to the end 
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Unformatted text preview: when it turned clear. 2) In the titration procedure part I the instructions tell you to rinse off the stirring rod used to break up the crystals. How would your results be affected if you did not do this? In part 2 adding KI too soon might result in the loss of I 2 by evaporation. How would this affect your answer? Well if I don’t rinse off the stirring rod, then the mass of the KIO3 decreases because it’s a waste of crystals, so then when the KIO3 decreases, the millimoles of KIO3 decreases which means a change in oxidation. If I add KI too soon, then the iodine will be lost because it will be vaporized and therefore the amount of thiosulfate would increase because then you would be titrating it more so for no reason, waiting for the reaction to happen....
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