Visualizing\nLe Chatelier’s Principle\nthrough Lead-EDTA Complexometric Titrations

Le Châtelier’s Principle is a concept that\nis taught\nin General Chemistry. Most instructional laboratory experiments demonstrating\nLe Châtelier’s Principle shift the equilibrium by temperature\nand use UV–vis absorption spectroscopy to characterize the\nchange. We present an EDTA complexometric titration to demonstrate\nLe Châtelier’s Principle while determining an aqueous\nlead ion concentration. The titration consists of two connected equilibria\nwhich shift according to Le Châtelier’s Principle throughout\nthe titration. The lead(II) hydroxide solids dissolve to produce free\nlead(II) ions which can bond with the EDTA. The shifting equilibria\ncan be seen in real time by the dissolution of lead(II) hydroxide\nand the color shifts of the indicator. We also discuss a real world\napplication of determining an aqueous lead(II) ion concentration via\nthis titration. The students were asked four postlaboratory questions\nrelated to the reactions and Le Châtelier’s Principle.\nA real world application of the titration is also provided.