Liquid Junctions and Elimination of Junction Potentials

Cells with Liquid Junctions and Elimination of Junction Potentials. When electrochemical cells are employed to obtain thermodynamic data, high accuracy ( 0.05 mV) requires the use of cells that are free from liquid junction (in the sense that the construction of the cell does not involve bringing into contact two or more distinctly different electrolyte solutions). Otherwise, the previously discussed uncertainties in the calculation of liquid-junction potentials will limit the accuracy of the data. 

The difference between cells with and without liquid junctions is one of degree rather than of kind. The cell used to establish the mean ionic activity coefficients of HC1 

TABLE 5.1 Computed Potentials of the Liquid Junction in Cells of the Type Ag AgCl MCl(Ci) MCl(C2) AgCl Ag 

In addition, a solution of pure hydrochloric acid might be present between the two saturated solutions. In this particular case, the considerations outlined in previous sections would lead us to believe that the liquid-junction potential in such a cell is negligible. If, however, hydrogen and silver chloride were more soluble, the resulting liquid-junction potential might not be negligible. 

Several types of cells of necessity involve liquid junctions. Examples9 include (1) half-cells of the second kind 

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