Freshening up Old Methods for New Students: A Colorful Laboratory Experiment to Measure the Formation Constants of Ni(II) Complexes Containing Ethane-1,2-Diamine

This is an easy and inexpensive laboratory experiment in which undergraduate students at the Bachelor's degree level in Chemistry can measure formation constants of complexes [Ni(en)n(OH2)6-2n]2+(n = 1, 2 or 3; en = ethylenediamine) through an acid-base titration. The background information necessary to understand the activity involves familiarity with equilibria and basic coordination chemistry, and the lab experience uses only common glassware and a pH meter. The mathematical treatment of the results is based on Bjerrum's formation function. Details of the activity, including full procedural and experimental data, are provided. The experiment can be augmented with additional work based on Job's method to analyze the stoichiometry of the complexes under investigation.