Activity from Measurement of Cell Potentials

Although potential measurements are used primarily to determine activities of electrolytes, such measurements can also be used to obtain information on activities of nonelectrolytes. In particular, the activities of components of alloys, which are solid solutions, can be calculated from the potentials of cells such as the following for lead amalgam  

In this cell, two amalgams with different mole fractions of lead act as electrodes in a common electrolyte solution containing a lead salt. The activities of lead in these amalgams can be calculated from emf measurements with this cell. 

DETERMINATION OF NONELECTROLYTE ACRVITIES AND EXCESS GIBBS EUNCRONS 

If we adopt the convention of writing the chemical reaction in the cell as occurring so that electrons will move in the outside conductor from left to right, so that the reaction in the left electrode is an oxidation and the reaction in the right electrode is a reduction, the reaction at the left electrode is 

As the electrolyte containing Pb is common to both electrodes, the cell reaction, that is, the sum of Reactions (17.17) and (17.18), is 

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