The Silver Indicator Electrode

In Chapter 14, we learned that the voltage of an electrochemical cell is related to the concentrations of species in the cell. We saw that some cells could be divided into a reference electrode that provides a constant electric potential and an indicator electrode whose potential varies in response to analyte concentration. 

Chemically inert platinum, gold, and carbon indicator electrodes are frequently used to conduct electrons to or from species in solution. In contrast with chemically inert elements, silver participates in the reaction Ag + e Ag(5). 

The reference half-cell potential ( , not E-) is constant at 0.241 V because [CP] is fixed by the concentration of saturated KCl. The Nemst equation for the entire cell is therefore 

E = reference electrode potential with actual concentrations in the reference cell 

E° = standard potential of reference half-reaction when all species are in their standard states (pure solid, pure liquid, 1 M, or 1 bar) 

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Figure 15-1 shows how a silver electrode can be used in conjunction with a saturated calomel reference electrode to measure [Ag ] during the titration of halide ions by Ag" (as shown in Figures 6-4 and 6-5). The reaction at the silver indicator electrode is... 

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