Nonpolarizable interface, salt

Nonpolarizable Interface. It is important to realize that in the case when only one salt of the type B1A1 is present, at respective concentrations ca and in phases a and P, as in the cell... 

This system behaves like a nonpolarizable interface. The salt concentration ratio will not be affected by potential applied from an extraneous source. The equilibrium potential depends only on the standard potentials of transfer of the ions in particular, it does not depend on the initial concentrations (ca and cp) nor is it a function of the phase volumes. Therefore, if only one salt is present in a LL system, the system is not amenable to potentiometric studies. It is thus essential that a supporting electrolyte be present to observe a potentiometric response of a third ion. The need to have a supporting electrolyte is similar to the need of immobilized ions in an ion exchanger membrane of an ion-selective electrode it also explains why it is essential that a supporting electrolyte or physiological concentration of salts must be present in measurements that employ fluorescent dyes. 

Warren, G. L., and S. Patel, Electrostatic properties of aqueous salt solution interfaces A comparison of polarizable and nonpolarizable ion models./ Phys. Chem. B, 2008.112(37], 11679-11693. 

Consider a metal electrode consisting of a silver wire placed inside the body, with a solution of silver ions between the wire and ECF, supporting the reaction Ag" + e <— Ag. This is an example of an electrode of the first kind, which is defined as a metal electrode directly immersed into an electrolyte of ions of the metal s salt. As the concentration of silver ions [Ag" ] decreases, the resistance of the interface increases. At very low silver ion concentrations, the Faradaic impedance Zfaradaic becomes very large, and the interface model shown in Fig. 3(a) reduces to a solution resistance in series with the capacitance C. Such an electrode is an ideally polarizable electrode. At very high silver concentrations, the Faradaic impedance approaches zero and the interface model of Fig. 3(a) reduces to a solution resistance in series with the Faradaic impedance Zfaradaic. which is approximated by the solution resistance only. Such an electrode is an ideally nonpolarizable electrode. 

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