Simple and Automated Coulometric Titration of Acid Using Nonisolated Electrodes

Abstract

Coulometric titrations involve the quantification of analyte by measurements of current and time. In most coulometric titrations, the anode and cathode are placed in isolated cells that are connected by a salt bridge. By contrast, the experiments described here involve coulometric titrations (of acidic protons in solution) using a silver anode and graphite cathode placed in the same reaction vessel. The chemistry of the electrode reaction generating the reactant is described. This use of non-isolated electrodes allows for simplified experimental procedures (some of which are described) and faster titration times. Additional streamlining of the experiment is achieved by the use of MicroLab data acquisition instrumentation. This laboratory is appropriate for an analytical course.

A Comprehensive Teaching Laboratory Program on Titration Analysis: Transition from Classic to Modern Approaches

“…During the “titrating” phase, standard solutions are gradually added to the analyte solution until the chemical reaction attains the equivalence point. This can be executed using conventional glass burets, modern precise metering pumps, or even electrolyte in situ electrolysis (coulometric titration). , The equivalence point can be approximated by observing specific physical changes that accompany chemical equivalence. “Determining”, on the other hand, pertains to establishing the end point of a titration reaction, either by adding an appropriate indicator or by harnessing other instrumental analysis techniques.…”

Iodine Coulometry of Various Reducing Agents Including Thiols with Online Photocell Detection Coupled to a Multifunctional Chemical Analysis Station To Eliminate Student End Point Detection by Eye

“…1−13 These home-built instruments recommend either isolation of the anodic and cathodic electrodes or instrument simplification using nonisolated electrodes. 11,13,14 Coulometric analyses can be coupled to various end point detection methods to find the time in which titrations are finished. For example, colorimetric end point determinations require the use of chemical indicators that signal the completion of the analyte reactions.…”

“…Different titrants can be electrogenerated to determine electroactive species, acids and bases, and even complexing reactants. Iodine, bromine, hydroxide, and hydrogen ions have been reported in the literature. − These home-built instruments recommend either isolation of the anodic and cathodic electrodes or instrument simplification using nonisolated electrodes. ,, …”

“…Starch is used as the visual indicator when iodine is the electrogenerated titrant. ,,,, Twin polarized electrodes for biamperometric measurements have been used for cyclohexene, hydrazine, biologically active thiols, and carbimazole determinations. ,,, Some authors have used two or more different end point determination methods to compare their precision. Comparison of eye detection versus graphical analysis, potentiometry versus eye detection, potentiometry versus amperometry and eye detection, and spectrophotometry versus amperometry have all been published in this Journal and elsewhere. ,,− …”