Potentiometric Titrations:

By far the most common application of potentiometry is in the potentiometric titrations. In these titrations, the potential between appropriate indicator and reference electrode immersed in the sample is monitored during the titration. The titrations can be performed manually or with automatic titration equipment. The cell potential (or in pH titrations the pH) is plotted as a function of the volume of titrant. Consider a redox titration represented by,

R₁   +  O₂  ↔   O₁   +  R₂                                                               ... (1.43)

where R and O stand for the reduced and oxidized species respectively, the potential of such a system depends upon the ratio of [O]/ [R] (see the discussion in the Nernst Equation). If the above reaction (1.43) is stoichiometric we can plot the cell potential against the volume of titrant. Since the potential of the reference electrode remains constant, the variations of the potential of the indicator electrode are followed during titration and the end point is determined from the resulting titration curve. An indicator electrode should be such in which it responds to a component (which is, the reactant or the titrant or the product) used in the titration. An amount of the reactant is compute from the volume of titrant required to reach the equivalence point. The equivalence point is detected by an abrupt change in potential and can be determined by any of the following three procedures:

i)  tangential methods

ii)   first derivative methods

iii) second derivative methods