Determination of Cl and I in Water

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Determination of Chlorine and Iodine in Water Purpose: The purpose of this lab was to determine the amount of chlorine present in tap water and iodine present in an iodine solution. This was done by titrating a sodium thiosulfate with the tap water and the iodine. Because the concentration of sodium thiosulfate changes over time standardization had to be done on the solution to determine the exact concentration of the sodium thiosulfate at the time of the experiment. This was done by using a reaction between potassium iodate and sodium thiosulfate solution to determine the exact concentration of the sodium thiosulfate solution at the time of the experiment. Once the solution of sodium thiosulfate had been standardized the molarity of the solution was known and sodium thiosulfate could be used to titrate tap water and an iodine solution to determine the amount of chlorine in the tap water and iodine in the iodine solution. Procedure/ Observations: The first step of the experiment was to standardize the sodium thiosulfate solution. This was done by cleaning a 50 mL buret and rinsing it three times with sodium thiosulfate solution to ensure the surface of the buret was consistent with the sodium thiosulfate throughout. The buret was then filled with the sodium thiosulfate solution. The buret was monitored to ensure that the solution extended to the tip of the buret and that no air bubbles were present because both would cause an inaccurate titration. The initial volume of the buret was then recorded to the nearest .02 milliliter. A 25 mL pipette was then used to measure exactly 25 mL of the KIO3 solution into a clean 250 mL beaker. 40-50 mL of deionized water was then added to the solution as well as about.5 grams of solid KI. The solution was stirred until all of the solid KI had dissolved. 2 mL of glacial acetic acid were added to the

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