The half-cell and its associated electrode reaction may be represented as
The electrode potential is given by
and therefore depends on the chloride ion activity. The saturated calomel electrode (SCE) is the easiest
to prepare, although it is more temperature-sensitive than versions employing 1 or 0.1 M potassium
chloride.
Silver-silver Chloride Electrode
This consists of a silver wire, coated with silver chloride and in contact with a solution of potassium
chloride saturated with silver chloride. The solution is contained in a tube, the end of which is sealed
with a porous plug or disc to facilitate contact with the sample solution. The half-cell and associated
electrode reaction is represented by
The electrode potential is given by
Like the calomel electrode, the saturated KCl version of this electrode is the most convenient to
prepare.
6.1—
Potentiometry
Summary
Principles
Measurement of the potential of a galvanic cell, usually at zero current; cell potential governed by the
potential of an indicator electrode which responds to changes in the activity of the species of interest.
Instrumentation
Indicator and reference electrodes; potentiometer, pH meter or millivoltmeter; electronics and recorder
for automated systems.
Applications
Quantitative determination and monitoring of many species in solution over a wide range of
concentrations (10–^7 – 1 M); relative precision 0.1–5%. Titrations are especially useful for coloured or
turbid samples or for mixtures.