Spreadsheet Methodology for the Calculation of Equilibrium Diagrams Including Precipitation Reactions and Formation of Mixed Ligand and Polynuclear Hydroxo Complexes

Abstract

Solution equilibria diagrams are excellent tools for understanding chemical speciation in multireaction chemical systems. They are usually plotted using software packages that efficiently perform advanced calculations, giving the possibility to graphically visualize thermodynamic and composition information. However, this approach frequently leaves the students with a poor understanding of the underlying theory. In this work, a simple method that uses extended Ringbom’s side reaction coefficients, named the Method of Extended Ringbom’s Coefficients (MERC), is proposed for plotting distribution and predominance diagrams using Excel, such that when the formation of mixed ligand and polynuclear species is considered, the mass balance equation is solved by applying a simple numerical recipe based on Newton–Raphson’s technique using circular references. If precipitation reactions are considered, then a corrected conditional solubility is used to study chemical equilibria in saturated or unsaturated solutions, by simply using the IF conditional function of Excel. The wide scope of this methodology is shown by studying the speciation and analysis of the redox properties of the Cu­(II)/Cu­(I)/Cu system in aqueous media in the presence of ammonia, thiosulfate ions, and EDTA under different multibuffered conditions. Also, the learning achievements of two examples of the application of MERC in the classroom are discussed.

The Laboratory Skills Contest: An Activity to Improve and Evaluate Students’ Laboratory Practice through the Determination of Water Hardness

“…The determination of water hardness is a simple project in an analytical chemistry course, but it is not easy to complete it with high quality. , This is especially true with titration, as it is always subject to errors, including the ability to see a change in the color of an indicator signaling the end point of a titration; overestimating or underestimating the value on an instrument’s readout scale; and failing to calibrate the instrumentation. − Therefore, there is a need to be careful and patient to minimize errors. This activity gives students sufficient time to practice their skills.…”