Visualizing Le Châtelier’s Principle through Lead-EDTA Complexometric Titrations

Abstract

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