Abstract
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.
Highlights
An introduction to coordination chemistry typically includes the formation of metal complexes in solution, and their characterization
As in all fields of science, so too in inorganic chemistry, fundamental concepts should be always related to practical laboratory activity that illustrates key concepts
The determination of stepwise or cumulative formation constants, K or β, respectively, allows the quantitative characterization of equilibria in solution; this approach is extensively used by chemists in widely different disciplines, from analytical chemistry to metal technology
Summary
An introduction to coordination chemistry typically includes the formation of metal complexes in solution, and their characterization. The determination of stepwise or cumulative formation constants, K or β, respectively, allows the quantitative characterization of equilibria in solution; this approach is extensively used by chemists in widely different disciplines, from analytical chemistry to metal technology. The determination of K involves taking advantage of a range of spectroscopic and potentiometric techniques.[1−3] The latter are among the oldest methods for determining stability constants, and are still being used with much success. They are based on the pH-dependent competition between hydrogen ions and metal ions (Lewis acids) for a ligand (weak Lewis base). This experiment is relatively rapid, safe, cost-effective, and easy-to-use, using readily available chemicals and equipment
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