487 C mol–^1 ), and n the number of electrons involved in the electrode reaction. At 298.15 K RT/F In 10
= 0.059 158 V thus
If the activities of all reactants and products are unity,. Theoretical cell potentials can be
calculated using tabulated values of. For dilute solutions (< 10–^1 M) concentrations can be used in
place of activities, the error becoming insignificant below 10–^3 M.
Reference Electrodes
Electroanalytical measurements relating potential or current to concentration rely on the response of one
electrode only, the other ideally being independent of solution composition and conditions. The latter is
known as a reference electrode; two such electrodes having these properties and in common use are
based on calomel and silver–silver chloride respectively.
Calomel Electrode
The electrode consists of two concentric glass tubes, the inner one of which contains mercury in contact
with a paste of mercury, mercury(I) chloride (calomel), and potassium chloride. This is in contact with a
solution of potassium chloride in the outer tube which itself makes contact with the sample solution via
a porous frit, fibre or ground-glass sleeve (Figure 6.1).
Figure 6.1
Saturated calomel reference
electrode (SCE).