Theory of the Salt Bridge

Liquid-junction potentials introduce uncertainties in the results of certain physical measurements in which great accuracy is desired, for example, pH membrane potentials. Thus, it is desirable to find methods for reducing the magnitude of liquid-junction potentials in various systems. Salt bridges containing saturated solutions of KCl are utilized 

At 25°C, a saturated KCl solution is 4.2 normal. The application of Eq. (13-119) to the determination of the liquid-junction potential of the boundary of Eq. (13-127) results in 

The quantity pH is best defined operationally in terms of the method used for its evaluation. In general, a cell of the form 

The half-cell reaction occurring at the left electrode is 

the free-energy change for the cell reaction can be written 

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