Conductivity of Concentrated Solutions

Conductivities k of electrolytes are related to molar conductivities A, ion conductivities A, and ionic mobilities w(- by Eq. (57) 

The most spectacular feature of a conductivity-concentration function is its maximum, attained for every electrolyte if the solubility of the salt is sufficiently high. For electrolytes which do not show strong ion association, the maxima can be understood on the basis of the defining equation of specific conductivity at the maximum [205], yielding 

For attempts in the literature to rationalize the maximum, with reference to solvation, ion association, or viscosity of the electrolyte, see Ref. [15]. 

In the literature measurements are often given at only 1 mol kg-1 or 1 molL for some salts in various single or mixed solvents. These are not suitable for rationalizing results, because the conductivity maxima depend on the type of ions, solvent, solvent composition, and temperature. 

Results from conductivity measurements can be advantageously evaluated for every temperature and solvent composition using the nonlinear fit [206] 

Specific conductivity k of electrolytes is related to molar conductivity A, ion conductivity A.i, and ionic mobility m . 

The most spectacular feature of conductivity-concentration functions is their maxima, attained for every electrolyte if solubility of the salt is sufficiently high. 

Solid phase/ electrode Liquid phase/ electrolyte Method Species References 

Li LiAsEs - DIOX ETIR Li AsEy from LIAsE6, LI2C03, LI02C0R, LiOR, LI02CH [337] 

Li LiAsEs - MPC ETIR LI02C0R, LIOCH3, LIOC3H7, LI2C03 (at storage) [335] 

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The intrinsic properties of an electrolyte evaluated at low concentrations of the salt and from the viscosity and permittivity of the solvent also determine the conductivity of concentrated solutions. Various systems were studied to check this approach. The investigated parameters and effects were ... 

Many recent examples show the importance of ionic radii and solvation in the conductivity of concentrated solutions. Suffice it to refer to three examples from the literature. 

In contrast to points (l)-(3) of discussion, the effect of ion association on the conductivity of concentrated solutions is proven only with difficulty. Previously published reviews refer mainly to the permittivity of the solvent or quote some theoretical expressions for association constants which only take permittivity and distance parameters into account. Ue and Mori [212] in a recent publication tried a multiple linear regression based Eq. (62)... 

Kraus CA, Lucasse WW. (1921) The conductance of concentrated solutions of sodimn and potassimn in Hqitid ammonia. J Am Chem Soc 43 2529-2539. 

One of the most useful expressions of this type is given by Amis and Casteel for the specific conductivity of concentrated solutions ... 

The specific conductivities of concentrated solutions are by one order of magnitude higher than those of salts in water i 3-57 With increasing concentration the conductivity decreases and passes through a minimum for 0.04 M solutions. Transport number measurements on sodium solutions have shown that the equivalent conductance of the anion (the solvated electron) has a minimum value at 0.04 M, while the equivalent conductance of the metal ion decreases continuously with increase in concentration . The blue colour of dilute metal solutions is due to the short wave length tail of a broad absorption band with its peak at 15,000 A. The... 

Casteel JF, Amis EA (1972) Specific conductance of concentrated solutions of magnesium salts in water-ethanol system. J Am Chem Soc 17 55-5... 

However, in contrast to dielectric permittivity of solvents which can be estimated with an acceptable degree of precision [30], there is up to now no valid approach to estimate the viscosity of solvents [31] and its temperature dependence and the conductivity of concentrated solutions and its temperature dependence, especially not when the solvent blend shows a low dielectric permittivity. A remarkable approach for the calculation of conductivity of electrolyte solutions (lithium salts in organic carbonates) was published in 2005 [31]. With this approach it is possible to obtain conductivities without any... 

Conductivities of concentrated solutions are usually expressed by empirical equations with parameters having no physical meaning. A widely used the Casteel and Amis equation for specific conductivity curves, k(c) or tc(m), have four adjustable parameters a, b, and or maximum of specific... 

Many recent examples show the importance of ionic radii and solvation for the conductivity of concentrated solutions. Suffice it to refer three examples from the literature. Binary mixtures of dipolar aprotic solvents of sufficiently high permittivity such as butylene carbonate (BC),PC,EC, and AN show Stokes-Walden behavior [412, 413]. For Bu4NBr in AN/PC in the temperature range 75°C > > —35 °C a linear correlation /Cmax(At) is found [413], independent of temperature and solvent composition. The use of high-permittivity solvents belonging to the same class suppresses the effects due to strong selective solvation or effects due to changing association. 

A. Than and E. S. Amis, J. Inorg. Nucl. Chem., 31, 1685 (1969). The specific conductance of concentrated solutions of magnesium chloride in the water-ethanol system. 

Despite its initial successes, there were apparent deficiencies in Arrhenius s theory. The electrical conductivities of concentrated solutions of strong electrolytes are not as great as expected, and values of the van t Hoff factor i depend on the solution concentrations, as shown in Table 14.4. For strong electrolytes that exist completely in ionic form in aqueous solutions, we would expect i = 2 for NaCl, i = 3 for MgCl2, and so on, regardless of the solution concentration. 

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