CHAPTER 10 - OTHER ELECTROCHEMICAL METHODS

Abstract

This chapter describes some electrochemical methods. The electrochemical methods can be divided into two classes: (1) those in which the current causes a chemical reaction, including polarography, which is the most important electrochemical method, electrodeposition, and coulometry; and (2) those in which an electrical device is used to indicate an endpoint, including potentiometry, amperometry, the use of polarized electrodes—dead stop endpoint—conductimetry, and high frequency titration. Analysis by electrodeposition has been in use for about a hundred years; by far, the greatest use of it is in the determination of copper. The conductimetric titration and high frequency titration techniques depend on changes in electrical properties of the solution during the course of the titration. In conductimetric titration, the conductivity of a solution depends on the mobility of the ions present. During a titration, if very mobile ions disappear and are replaced by less mobile ions, then the conductivity will drop. In high frequency titration, the reaction takes place in a cell between two plates of a condenser so that the cell and its contents form a capacitor. This is coupled to a high frequency oscillator circuit—frequency several megacycles per second. Changes in the composition of the solution affect the electrical characteristics of the cell and these in turn produce changes in the oscillator circuit that can be measured.