Determination of Chlorine and Iodine in Water
The purpose of this laboratory was to determine the amount of chlorine and iodine in a sample of water by titration using a starch indicator and to standardize a sodium thiosulfate solution. Chlorine is added to municipal water supplies to purify it enough to become safe to drink. Iodine is also added to water when people camp or go hiking in the back country where they cannot bring purified water along. Chlorine and iodine are added to kill microorganisms in water. Oxidation reactions occurred in this experiment. The Chlorine was oxidized because it lost electrons in the reaction. The iodine was reduced because it gained electrons. The solutions turned a yellow color because of the iodine which disappears once all of the iodine has reacted in the titration. Sodium thiosulfate was the titrant in the process of titration. It was added to react with the iodine in the solution. Starch was added to give the solution a blue color near the endpoint of the titration. Potassium iodate (KIO₃) was used to standardize the sodium thiosulfate solution. Practical applications would include testing unknown samples of water and municipal water supplies for the concentration of chlorine present because too much can cause health problems and not taste well. Not enough added, wouldn’t kill the microorganisms in the water to make it safe to drink. II. Procedure
First the standardization of Sodium Thiosulfate was completed. A 50mL buret was obtained and rinsed twice with the sodium thiosulfate solution. It was then filled with the solution. The tip of the buret was checked to make sure there weren’t any bubbles in it. Then a 250mL beaker was obtained. A 25mL pipette was used to add exactly 25mL of the KIO₃ solution. Then 50mL of deionized water and about .25g of solid KI was added. The solution was stirred until the solid was completely dissolved. 2mL of glacial acetic acid was then added....
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