Question

Discuss the working of metal-insoluble salt electrode by taking a suitable example.

Answer 1

Electrodes of the second kind are metal electrodes assembly with the equilibrium potential being a function of the concentration of an anion in the solution. Typical examples are the silver/silver-chloride electrode and the calomel electrode.

Silver chloride electrode (Ag_(s)|AgCl_(s)|KCL_(H2O))

The electrode functions as a redox electrode and the equilibrium is between the silver metal (Ag) and its salt—silver chloride (AgCl, also called silver(I) chloride). It's potential is dependent only on concentration of cloride-anion.

The corresponding half-reactions can be presented as follows:

Ag⁺ + e^- = Ag

AgCl + e^- = Ag + Cl^-

This reaction is characterized by fast electrode kinetics, meaning that a sufficiently high current can be passed through the electrode with the 100% efficiency of the redox reaction (dissolution of the metal or cathodic deposition of the silver-ions). The reaction has been proven to obey these equations in solutions of pH values between 0 and 13.5.

The Nernst equation below shows the dependence of the potential of the silver-silver(I) chloride electrode on the activity or effective concentration of chloride-ions:

E=E⁰-(RT/F)ln(a_Cl-)