Testing Table Salt for its Potassium Iodide Content - Class Notes | CHEM 222, Study notes of Analytical Chemistry

Download Testing Table Salt for its Potassium Iodide Content - Class Notes | CHEM 222 and more Study notes Analytical Chemistry in PDF only on Docsity! Testing Table Salt for Its Potassium Iodide Content The Problem: Food stores sell both “regular” and “iodized” table salt, the latter containing a small amount of KI to help consumers avoid the illness known as goiter. Can we tell the difference between the two salts? Does the iodized salt contain the right amount of potassium iodide? Preparation: Prepare a 0.04 M sodium thiosulfate solution by dissolving 2.48 g of sodium thiosulfate pentahydrate in distilled water in a 250 mL volumetric flask. Dissolve and bring to volume line. Transfer 10.0 mL of this solution to a 100 mL volumetric flask, add distilled water to the volume line and mix. This solution is your 0.004 M thiosulfate solution. Place 20.0 g of regular salt in one 600 mL beaker and 20.0 g of iodized salt in another 600 mL beaker. Dissolve each in 200 mL of distilled water, ignoring slight insoluble residues. To each add 2 mL of bromine water and let stand for a few minutes. The yellow color of the excess bromine must be evident. Any iodide ion in the salt is thereby oxidized to iodate ion. +−−− ++→++ HBrIOOHBrI 6633 322 (1-1) To each beaker add 2 mL of formate buffer. This will reduce the excess bromine. +− ++→+ HCOBrHCOOHBr 22 22 (1-2) Then add about 3.0 g of KI to each beaker. The iodized salt will show a much darker yellow color due to the formation of triiodide ion when the iodate ion is reduced by the iodide in acidic solution. OHIIHIO 233 3386 +→++ −−+− (1-3) Add 2 mL of starch indicator to the iodized salt solution and titrate with 0.004 M sodium thiosulfate solution. −−−− +→+ 264 2 322 32 OSIOSI (1-4) Calculate the percent KI in the iodized salt.