Complexation Effect on Redox Potential of Iron(III)−Iron(II) Couple: A Simple Potentiometric Experiment

A titration curve with multiple inflection points results when a mixture of two or more reducing agents with sufficiently different reduction potentials are titrated. In this experiment iron(II) complexes are combined into a mixture of reducing agents and are oxidized to the corresponding iron(III) complexes. As all of the complexes involve the iron(III)−iron(II) couple, it is the complexation or ligand effect that causes speciation of iron as different reducing agents. These experiments illustrate the stabilities of iron(III)−iron(II) complexes with EDTA, water, and o -phenanthroline ligands.