Coulometric Titration Experimental Practice for Undergraduate Laboratories: A 1960s Twist to a Modern Coulometer

Abstract

When teaching quantitative analytical chemistry to undergraduate students, the transitions from classical analytical methods to instrumental ones can be tough as most (if not all) of the visual/sensorial aspects of the analyses (solution color and volume and mass changes) are lost in the instrumental interface. We have observed that the loss of these aspects can have a significant impact on a student’s ability to understand instrumental methods. Coulometric titrations offer a seamless transition path between classical and instrumental methods, offering several parallels between them, especially if visual indicators are used for determining the titration endpoint, and could be used in undergraduate laboratories to facilitate this transition. Unfortunately, modern instrumentation used for coulometric titrations does not offer a hands-on experience for the user, widening the gap between this technique and classical methods and limiting the use to bridge both. Here, we report on the fabrication of a simple and affordable instrumentation that brings back the hands-on interface of a 1960s coulometer to a modern potentiostat/galvanostat and its application to an undergraduate teaching laboratory for the coulometric titration of ascorbic acid using iodine and starch solution as a visual indicator. Molecular absorption spectra are used to quantify the student’s increased accuracy in identifying the titration endpoint closer to the equivalency point with successive titrations, demonstrating important didactic aspects of this experimental practice and granting it a place in most chemistry undergraduate curriculums.