Limiting equivalent ionic conductances

Table 8.32 Limiting Equivalent Ionic Conductances in Aqueous Solutions 8.157...

In Section 8, the material on solubility constants has been doubled to 550 entries. Sections on proton transfer reactions, including some at various temperatures, formation constants of metal complexes with organic and inorganic ligands, buffer solutions of all types, reference electrodes, indicators, and electrode potentials are retained with some revisions. The material on conductances has been revised and expanded, particularly in the table on limiting equivalent ionic conductances. 

Hence the decrease of AgN03 concentration within the catholyte is exactly equal to its increase within the anolyte, which for this symmetrical type of cell is to be expected therefore, only one of the two needs to be measured in order to determine the transference numbers. From the transference numbers and the limiting equivalent conductivity A0, one obtains the equivalent ionic conductivities Aq = tg A0 and Aq = tg A0. 

The magnitude of the dissociation constant A plays an important role in the response characteristics of the sensor. For a weakly dissociated gas (e.g., CO2, K = 4.4 x 10-7), the sensor can reach its equilibrium value in less than 100 s and no accumulation of CO2 takes place in the interior layer. On the other hand, SO2, which is a much stronger acid (K = 1.3 x 10-2), accumulates inside the sensor and its rep-sonse time is in minutes. The detection limit and sensitivity of the conductometric gas sensors also depend on the value of the dissociation constant, on the solubility of the gas in the internal filling solution, and, to some extent, on the equivalent ionic conductances of the ions involved. Although an aqueous filling solution has been used in all conductometric gas sensors described to date, it is possible, in principle, to use any liquid for that purpose. The choice of the dielectric constant and solubility would then provide additional experimental parameters that could be optimized in order to obtain higher selectivity and/or a lower detection limit. 

In nonsuppressed IC, eluent competing ions of low limiting equivalent ionic conductance,47 such as carboxylate, are required. In suppressed IC, the mechanism of suppression dictates the choice of an eluent. In the case... 

Table 4.1. Limiting equivalent ionic conductances in aqueous solution at2.5°C. Units ohm cm cquiv [1].

Table 2 Limiting equivalent ionic conductances (S cm equiv ) of ions in aqueous solutions...

For a weakly ionized substance, A varies much more markedly with concentration because the degree of ionization a varies strongly with concentration. The equivalent conductance, however, must approach a constant finite value at infinite dilution, Ag, which again corresponds to the sum of the limiting ionic conductances. It is usually impractical... 

Values of limiting molar ionic conductivities for a few common ions are shown in Table 1. The data tabulated are referred to 25°C temperature. The term limiting molar ionic conductivity is used according to lU-PAC recommendation, rather than the formerly used limiting ionic equivalent conductivity. The molar and equivalent values are interconvertible through stoichiometric coefficient z. 

When the polymer flhn is oxidized, its electronic conductivity can exceed the ionic conductivity due to mobile counterions. Then, the film behaves as a porous metal with pores of limited diameter and depth. This can be represented by an equivalent circuit via modified Randles circuits such as those shown in Figure 8.4. One Warburg element, representative of linear finite restricted diffusion of dopants across the film, is also included. The model circuit includes a charge transfer resistance, associated with the electrode/fllm interface, and a constant phase element representing the charge accumulation that forms the interfacial double... 

The ionic transport in solids is attributed to the hopping of ionic carriers between the equivalent positions in the crystal lattice. This mechanism is known as lattice diffusion and depends on the jumping distance and frequency of moved ions. The understanding of the influence of these factors on the ionic conductivity is very important for the development of material with enhanced ionic transport. The question of what is the limit of ionic conductivity in solids will be addressed by analyzing the ionic transport in cubic stabilized zirconia systems with different acceptor dopants. 

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