SOLUBILITY MATTERS-MEASURING THE KSP OF CALCIUM IODATE

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Students use an unusual titration technique to determine the equilibrium constant for the solubility of calcium iodate in water. Sodium thiosulfate solution is added dropwise from a pre-weighed bottle to a saturated solution of calcium iodate that has been mixed with excess potassium iodide. The iodate/iodide reaction generates elemental iodine, which undergoes reduction when sodium thiosulfate is added. Starch is used as an indicator—the tell-tale blue color of the starch/iodine complex disappears instantly at the endpoint of the titration. Students calculate the concentration of iodate ion, the concentration of calcium ion and, finally, the solubility product constant—K_sp value—for calcium iodate. Equilibrium constant calculations do not have to be abstract, mind-numbing, number-crunching exercises. Let your students see where the numbers come from and what the numbers mean! Includes reproducible student handouts, detailed background information, complete Teacher Notes with sample data and answers to all questions and all necessary chemicals and consumable supplies.

Complete for 30 students working in pairs. Fifteen reusable serological pipets and pipet bulbs are recommended and available separately.