Ascorbic Acid Report.docx - Chemistry Lab 114 R5 Analysis...

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Chemistry Lab 114 – R5Analysis of Ascorbic Acid by Redox Titration: A Green Chemistry ExperimentPurposeThe purpose of this experiment is to perform a quantitative analysis of ascorbic acid (C6H8O6),commonly known as Vitamin C, by a redox titration. The reaction of interest in this experimentis between ascorbic acid and a water-soluble form of iodine (I3-) which serves as the oxidizingagent. The concentration of ascorbic acid in the unknown sample is calculated from both thevisual endpoint and the potentiometric endpoint.TheoryThe theory behind this experiment is to utilize the conductivity curve of the titration of ascorbicacid with water-soluble iodine to find the inflection point, which represents the potentiometricendpoint. This inflection point is then used to calculate the concentration of ascorbic acid in theunknown sample, which is compared to the concentration value calculated from the visualendpoint noted during the titration. In the titration reaction, carbon atoms from ascorbic acid areoxidized and iodine is reduced. The reaction produces tri-iodide ions, which steadily decreaseand then increase in concentration throughout the titration. The changes in concentration of thetri-iodide ions are recorded in the conductivity graph of the titration, which is ultimately used tocalculate the final concentration of ascorbic acid in the unknown sample. The voltage changesmost rapidly near the endpoint, which is why small additions of iodine titrant at this point arerequired for accurate results. As previously mentioned, the titration reaction also produces avisual endpoint. The indicator used in this experiment is 2% starch solution. When all of theascorbic acid in the unknown sample has been oxidized by the iodine, the next drop of iodinetitrant reacts with the starch indicator to produce a dark blue-black color, which signals the visualendpoint. The concentration value calculated from the visual endpoint is then compared foraccuracy to the concentration value calculated from the potentiometric endpoint.

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Term
Fall
Professor
N/A
Tags
Green Chemistry, Redox, unknown sample, visual endpoint, iodine titrant solution

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