2CLabManual201303

The polymeric amylose starch molecules wrap

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Unformatted text preview: er all of the ascorbic acid in the sample of interest has been consumed. The titration flask initially contains some added KI and starch solution. The first small excess of NBS oxidizes some iodide ions to molecular iodine, which then reacts with more I- to produce the triiodide ion, I3-. The polymeric amylose (starch) molecules wrap themselves around the triiodide ions and form a blue colored aggregate to signal the endpoint. Ascorbic acid solutions are susceptible to air oxidation, which can be inhibited in various ways, including acidification. The air oxidation of ascorbic acid is catalyzed by metal ions increasing the rate of degradation of ascorbic acid significantly. Oxalic acid forms complexes with most metal ions and prevents their functioning as an oxidation catalyst. Oxalic acid is commonly employed to increase the longevity of ascorbic acid. The last segment of this experiment will test these factors involved in the degradation of ascorbic acid. Please read the appropriate chapter in your textbook, as pre-laboratory preparation for this expe...
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This note was uploaded on 04/09/2013 for the course CHE CHE 2C taught by Professor Nasiri during the Spring '07 term at UC Davis.

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