Ionic equivalent conductance

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. 

Figure 16.1 Simple dry cell battery. Electrons are conducted along the external circuit (4), which physically connects the active (2) and noble (1) materials. An equivalent ionic counter-current is conducted through the electrolyte (3), thereby completing the circuit.

Salts such as silver chloride or lead sulfate which are ordinarily called insoluble do have a definite value of solubility in water. This value can be determined from conductance measurements of their saturated solutions. Since a very small amount of solute is present it must be completely dissociated into ions even in a saturated solution so that the equivalent conductivity, KV, is equal to the equivalent conductivity at infinite dilution which according to Kohlrausch s law is the sum of ionic conductances or ionic mobilities (ionic conductances are often referred to as ionic mobilities on account of the dependence of ionic conductances on the velocities at which ions migrate under the influence of an applied emf) ... 

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. 

Sometimes in the literature the equivalent ionic conductivity at infinite dilution is erroneously termed ion mobility however, eqn. 2.17 clearly shows the interesting linear relationship between both properties with the faraday as a factor. 

EQUIVALENT IONIC CONDUCTIVITIES AND ION MOBILITIES AT INFINITE DILUTION IN AQUEOUS SOLUTIONS AT 25° C... 

In the ideal case, the ionic conductivity is given by the product z,Ft/ . Because of the electrophoretic effect, the real ionic mobility differs from the ideal by A[/, and equals U° + At/,. Further, in real systems the electric field is not given by the external field E alone, but also by the relaxation field AE, and thus equals E + AE. Thus the conductivity (related to the unit external field E) is increased by the factor E + AE)/E. Consideration of both these effects leads to the following expressions for the equivalent ionic conductivity (cf. Eq. 2.4.9) ... 

Wagner s solution See Wagner s reagent. vag narz sa.Iu shan 1 Walden s rule phys chem A rule which states that the product of the viscosity and the equivalent ionic conductance at infinite dilution In electrolytic solutions is a constant, independent of the solvent It Is only approximately correct. wol-danz, rul ... 

Ccen designates the cell constant (/fcen = d/A). Its value cannot be obtained by direct measurement, but is determined using a standard solution for which the conductivity k is known. The equivalent ionic conductance (S m 2 mol 1) refers to the conductivity of an ion with a valence of z in a solution at 25 °C when the molar concentration C (mol I 1) tends towards 0 (Table 4.1). 

Table 4.1—The equivalent ionic conductivities at infinite dilution in water at 25 "C...

The mobility u and diffusion coefficient D of an ion are two of the trio of transport parameters of which the third is the equivalent ionic conductivity X. Conductivity is not a topic here and we will merely quote the... 

The equivalent ionic conductance of e aq was determined as 170 ( 15) from which the mobility of e aqy y.e = 1.77 X 10 3 cm2/v/sec. (In this determination a given error in a G value or a rate constant introduces only a much smaller error into the equivalent ionic conductance of e aq.) Since De and y.e are related by the expression... 

The contribution of the individual ion i to the equivalent conductivity A of the electrolyte is called equivalent ionic conductivity (A) where A = unit conductivity/ concentration. For simple uni-univalent electrolytes, such as Na+, CP, we can write for the individual contributions of the anion and cation... 

In general, for mixed valency electrolytes, we can express the individual transference numbers in terms of the experimentally accessible equivalent ionic conductivities from (6.17) and (6.19) as... 

For a uni-univalent electrolyte, the multiplier term in (6.24) cancels out and the liquid junction potential can be calculated from the equivalent ionic conductivities Xi of the two solutions, from the Sargent equation. 

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... 

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