Jelly Potentiometry, Do It Yourself

Abstract

Understanding potentiometry is a difficult task when students in initial courses of Analytical Chemistry are first introduced to instrumental techniques. The closest instrument to them is a pH meter, which is frequently used as a “black box”, without a real understanding of how it works. Here we present the assembly of jelly modules that the students can combine in different ways with the purpose of visualizing what reference and indicator electrodes are and their function when they are used in potentiometric measurements with quantitative purposes. This didactic sequence was used during six semesters in a first course of Analytical Chemistry dictated for students becoming laboratory technicians in Chemistry and Chemical Engineering. It is a hands-on experiment to exemplify both a direct potentiometric analysis and a potentiometric titration (indirect analysis). It is simple, low-cost, and easy to apply. It only requires gelatin, salts, pieces of metal, and a multimeter. The students showed interest in its execution, and they were able to identify the functions of the electrodes, discuss the different analytical implications of potentiometric techniques among themselves, and make the requested graphics with very good results.