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Unformatted text preview: ration of the iodine solution with the sodium thiosulfate.
• Titrate the iodine solution with the sodium thiosulfate solution you have made.
Do not add the starch indicator until the titration is almost finished.
• As you perform the titration, the solution color should go from brown to yellow.
Once the solution fades to a light yellow you should add the starch indicator. This
sharpens the endpoint.
In concentrated iodine solutions, the starch complex can tie up some of the
dissolved iodine molecules, effectively removing them from the titration and
affecting the accuracy of the results.
• Do at least three trials. Perform the titration immediately upon mixing the
chemicals. Though it is tempting to use "assembly line" techniques and prepare
all of your flasks at once and then titrate them all, this can also adversely affect
your results. The iodine in the solution can clump together over time and become
more and more difficult to dissolve.
• Report your average molarity of Na2S2O3 standardized solution, and stan...
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- Spring '07