A Variety of Electrochemical Methods in a Coulometric Titration Experiment

An experiment for a practical course is described in which the amounts of HCl and KI in a mixture of standardized solutions are determined by three coulometric titrations. The iodide content is titrated with bromine that is generated at the anode from bromide which oxidizes the I^- to I₂ and further to IBr^2-. The titration is followed with a twin-polarizable platinum electrode which essentially records the I₂ and (after the endpoint) Br₂ levels. Analysis of the chloride content is performed indirectly by titration of the acid through cathodic reduction of H⁺ to H₂. The titration is monitored with a glass electrode. Finally I^- and Cl^- are determined simultaneously by anodic dissolution of a silver wire with a silver electrode recording the course of the titration. The experiment provides an internal check of the quality of the analysis and presents a variety of electrochemical methods of pedagogical value. Hints for the practical performance of the experiment in laboratory courses are given, and the necessary electronic circuits for self-assembling are described. Laboratory experiences with students' data collection by hand, recorder and computer are dealt with in this experiment. A complete list of earlier papers is provided, which can be found in this Journal, on the subject of coulometric analysis.