The Measurement of Electrode Potentials

Experiments have shown that the magnitude of the electrode potential changes when the concentration of the aqueous solution (or the partial pressure of any gas involved in the cell reaction) is altered.

Therefore, electrode potentials are normally measured under standard state conditions (using 1.00-M solutions, and gas pressures of 1.00 atm.). When measured in this way, the cathode potential is termed the Standard Electrode (or Reduction) Potential.

Of course, Standard Electrode Potentials cannot be measured independently, since no cathode reaction can be made to occur in the absence of an anode reaction (which provides electrons for the anode reaction).

How then are Standard Electrode Potentials measured?

By measuring them all relative to one particular anode reaction. In this way, all standard cathode potentials can be placed on a common scale.