Reaction Stoichiometry (Complex Ion Formation)

Not carried out.

Students study the formation of complex ions by reaction of metal ions with ligands that bind to them. Absorption spectra for each complex ion are measured for a series of solutions prepared by mixing various amounts of metal ion solutions and ligand solutions. Each pair of students prepares and measures several solutions to help produce large numbers of results in a relatively short time. These are combined and readily analyzed to reveal the reaction stoichiometry and thus the composition of complex ions.

Since a number of results form multiple students are combined in this experiment, it is important to be able to judge their quality and weed out erroneous ones. For this purpose, it is helpful that the entire spectrum is recorded for each prepared solution. Any problems caused by improper sample positioning, etc., are obvious from non-zero baselines and those measurements can be quickly repeated. Reporting the value for the wrong wavelength is also obvious and can be corrected. This is not so straightforward if combining results from numerous students employing single-wavelength Spectronic 20s, since nothing is reported but an absorbance value (hopefully at the correct wavelength and properly measured!).