Testing Table Salt for KI Content By: Stephanie Njegovan

Prepare 0.04M sodium thiosulfate solution (250mL) Weigh out 2.48g of sodium thiosulfate pentahydrate Transfer to 250mL volumetric flask Dissolve in distilled water Dilute to mark and mix well.

Dilute to 0.004M sodium thiosulfate solution (100mL) Transfer 10.0mL of the 0.04M solution, just made, to a 100mL volumetric flask Dilute to 100mL line with distilled water and mix thoroughly This is the solution we will later be using for titration!!

Regular vs. Iodized Weigh out 20.0 g of regular salt. Weigh out 20.0 g of iodized salt. Transfer each salt into separate 600mL beakers, making sure to label each accordingly. Regular Iodized

Add water & bromine H20… Using a graduated cylinder, add 200mL of distilled water to each beaker to dissolve salt Add 2mL of already prepared bromine water to each beaker and let stand for a few minutes At this point, the solutions must be yellowish, indicating an excess of bromine Any iodide in the salt is oxidized to iodate ion I- + 3Br2 + 3H20  IO3- + 6Br- + 6H+

Add formate buffer & KI… To each beaker, add 2mL of formate buffer to reduce the excess bromine. Br2 + HCOOH  2Br- + CO2 + 2H+ Add ~3.0g KI to each beaker The iodized salt will be a darker yellow because the triiodide ion forms when the iodate ion is reduced by the iodide in acidic solution IO3- + 6H+ + 8I-  3I3- + 3H2O

Add starch & titrate! Add 2mL starch indicator to the iodized salt solution Finally, titrate each solution with 0.004M sodium thiosulfate solution, that was made in the first steps, to complete the experiment I2- + 2S2O42-  3I- + S4O62-

Test your knowledge.. What was the purpose of adding 2mL of formate buffer to the salt solution? The formate buffer reduces the excess bromine in the salt solution (from the bromine water).