The relative stabilities of a number of copper(II) and nickel(II) complexes are visually compared by noting color changes that result from ligand exchange reactions. The demonstration illustrates the chelate effect: the increased stability of bidentate ligands over monodentate ligands and in one case, the increased stability of a tetradentate ligand over a bidentate ligand. By carrying out the reactions on an overhead projector, they can be shown to a larger audience of students. The roles that enthalpy and entropy play in the chelate effect are discussed.
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