10.4 : Potentiometry: Overview

Potentiometry is an analytical technique that measures the potential difference between two electrodes in an electrochemical cell without drawing any significant current that could alter the solution's composition. This method employs an indicator electrode, which exchanges electrons with the analyte solution, and a reference electrode with a constant potential. Each electrode is immersed in a solution comprised of two half-cells. In a conventional setup, the reference electrode serves as the anode (left-hand electrode), the site of oxidation where electrons are lost, while the indicator electrode acts as the cathode (right-hand electrode), where reduction occurs and electrons are gained. These half-cells are connected through a salt bridge, typically filled with an inert electrolyte, to prevent short-circuiting and mixing solutions. The cell potential is determined by calculating the difference between the reduction potentials—a measure of the tendency of a substance to gain electrons— at the cathode and anode. To ensure accurate measurements in cells utilizing salt bridges, liquid junction potentials that develop at interfaces between dissimilar electrolyte solutions must be considered. However, these effects can be reduced by maintaining balanced ion mobilities and high salt concentrations.

The Nernst equation can estimate the analyte concentration, but for more precise measurements, factors such as temperature dependency and matrix effects must also be accounted for. Overall, potentiometry is a valuable technique for analyzing various solutions and determining their chemical compositions.