Saturated calomel electrode

The calomel electrode ( SCE, English:. Saturated Calomel Electrode, SCE ) is an electrode of the second kind

Construction

A calomel electrode consists of mercury, which is coated with sparingly calomel ( Hg2Cl2 ) and immersed in a saturated potassium chloride solution. With the analysis solution contact via a diaphragm ( semipermeable membrane) or a liquid film can be produced in a ground glass stopper.

The cell notation of the saturated calomel electrode is:

Principle of operation

The potential-determining electrode reaction is the equilibrium between the metal in the electrode and metal ions in the KCl solution:

The potential of the electrode E, is described by the Nernst equation, where E ° is the standard potential of the electrode reaction, R is the universal gas constant, T is the thermodynamic temperature and F is the Faraday constant:

For the solubility equilibrium applies:

The solubility product, KL, making it thus:

The equation of the solubility can be used for the concentration of mercury in order to obtain the potential alone, depending on the chloride concentration:

KL - term as the standard potential, only dependent on the temperature. It is therefore useful to him in a newly defined standard potential, which involve the calomel electrode: