Junction Potential Between Electrolyte Solutions in the Same Solvent

Liquid Junction Potential Between Electrolyte Solutions in the Same Solvent 

If two electrolyte solutions that are of different concentrations but in the same solvent contact each other at a junction, ion transfers occur across the junction (Fig. 6.3). If the rate of transfer of the cation differs from that of the anion, a charge separation occurs at the junction and a potential difference is generated. The potential difference tends to retard the ion of higher rate and accelerate the ion of lower rate. Eventually, the rates of both ions are balanced and the potential difference reaches a constant value. This potential difference is called the liquid junction potential (LJP) [10]. As for the LJP between aqueous solutions, the LJP between non-aqueous solutions can be estimated using the Henderson equation. Generally the LJP, Lj-, at the junction Ci MX(s) c2 NY(s) can be expressed by Eq. (6.1)  

In electrochemical measurements in non-aqueous systems, we sometimes use a cell with a junction between electrolyte solutions in different solvents. The problem of the LJP between different solvents is rather complicated but is discussed in Section 6.4. 

The pH scale in non-aqueous solutions was briefly discussed in Chapter 3. In this section, practical methods of pH measurements in non-aqueous systems are considered, with emphasis on the differences from those in aqueous solutions. 

Because Eq. (6.2) contains a single ion activity, which is thermodynamically indeterminable, we have to define an operational pH scale. According to the IUPAC proposal [11], it is defined by (1) and (2) below. 

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