Walden products, ionic

Conductometric and spectrophotometric behavior of several electrolytes in binary mixtures of sulfolane with water, methanol, ethanol, and tert-butanol was studied. In water-sulfolane, ionic Walden products are discussed in terms of solvent structural effects and ion-solvent interactions. In these mixtures alkali chlorides and hydrochloric acid show ionic association despite the high value of dielectric constants. Association of LiCl, very high in sulfolane, decreases when methanol is added although the dielectric constant decreases. Picric acid in ethanol-sulfolane and tert-butanol-sulfolane behaves similarly. These findings were interpreted by assuming that ionic association is mainly affected by solute-solvent interactions rather than by electrostatics. Hydrochloric and picric acids in sulfolane form complex species HCl and Pi(HPi). ... 

Ionic Walden Products. Fundamental work by Kay and Evans (22) has shown that a correct interpretation of the conductometric behavior of ions in water cannot be made without considering both the complex three-dimensional structure of water and the structure-breaking, structure-making properties of ions. On the other hand, if water is an atypical... 

Figure 2. Ionic Walden products normalized to their values in water as a function of mole percent organic solvents (- ), tert-Bu0H-H20 ...

Ionic liquid System Cation Anion(s) Temperature, (X Conduc- tivity (k), mS cm Conduc- tivity method Viscosity (n), cP Viscosity method Density (p), gcm Density method Molar conductivity fAJ, cm iT mor Walden product (An) Ref. 

Table 2. Concentration c, conductivity

This equation is known as Walden s rule. The constant is called the Walden product. Although the salt contents of bulk ILs are very high (about 3-7 mol L-1), the Walden plots for a variety of ILs are similar to that of a conventional diluted system [113]. This observation indicates that ILs are ionized effectively, even in the bulk. However, ILs also contain ion aggregates which do not contribute to the ionic conductivity. Recent research shows more specifically how much ILs are ionized [114]. 

Let us now consider inorganic ionic behavior. Na+ shows R values greater than unity throughout almost the entire range of the solvent composition with a maximum at about 30 mol % TMS. Cl" and Br", up to 60 mol % in TMS, possess nearly constant values, and are roughly equal to those in water, while I" and C104", which are the best structurebreaking ions in water, show a minimum in Walden products at about 10 mol % TMS. Therefore Na+, contrary to anions, behaves in water-TMS as it does in the mixtures studied by Kay and Broadwater. 

Table 1. Partial Molar Volume (Vj°°). Effective Ionic Radius (rjf), Stokes Radius (rs), and Temperature CoefScient of Walden Product (dln( A °°Tj ldT) at 25 ...

Ionic liquid system Cation Anion(s) Temperature (K) Conductivity (K), mS cm 1 Conduc- tivity method Viscosity (V), CP Viscosity method Density (Pi, g c 3 Density method Molar Conductivity (A), cm2 Q -1mor7 Walden product (M) Ref. 

A test of Stokes equation is easily arranged. Table 5.12.1 lists sets of ionic radii, and Table 5.12.2 the so-called Walden products A° 7 for several cations and anions using data drawn from Appendices 5.12.1 to 5.12.12. The first point to notice is that the Walden product for a given ion varies from solvent to solvent and attains approximate constancy only when the ion is very large. In most cases, therefore, the Stokes radius is a function of the solvent as well as of the ion. For ranges... 

The two indirect methods of estimating ionic conductances are closely related. Equally mobile ions must have equal Walden products. Table 5.12.2 has shown that Walden products even of fairly large ions vary somewhat from solvent to solvent, and it is only a certain parallelism in these variations that gives a reference electrolyte a better chance of succeeding. For example, the Walden productsofBu4N and of Pic" are both ca. 33 % greater in NMA than in water, but the ratios of their Walden products, and of their conductances, differ by only 1 % in these two media. The correlation in other instances is far from perfect, however, and Table 5.12.2 makes it plain that it cannot always be relied... 

EFFECT OF PRESSURE ON CONDUCTANCE. II. WALDEN PRODUCTS AND IONIC ASSOCIATION IN METHANOL. 

Another assumption for the determination of ionic conductivities uses Walden s rule [7], which correlates the conductivity of ions in different solvents with the help of the respective viscosities. Using this assumption, Krumgalz [8] proposed the apparent constancy of the Walden product for various ions in different solvents... 

A Stokes radius may be assigned to an ion, "ist = F I )%Njf) Zi lri. Ionic Stokes radii are commensurate with ri but not directly related to them for some ions even rist < i, although they ought to be larger, pertaining to the hydrated ions. The Walden products are approximately... 

The conductivity of electrolytes and ionic limiting conductivities in mixed solvents are intimately related to the viscosities of these solutions according to the concept of the Walden product A°°t] = const for a given electrolyte (ion) irrespective of the temperature and the solvent or mixed solvent composition. 

Huyskens PL, Lambeau YO (1978) Ionic conductances and Walden products of anions mono- and dissolvated by citric acid in acetonitrile. J Phys Chem 82 1892-1897 Apelblat A, Neueder R, Barthel J (2006) Electrolyte data collection. Electrolytic conductivities, ionic conductivities and dissociation constants of aqueous solutions of organic dibasic andtribasic acids. Chemistry Data Series, vol XII, Part 4c. Dechema, Frankfurt Lee WH, Wheaton RJ (1978) Conductance of symmetrical, unsymmetrical and mixed electrolytes. Part 2. Hydrodynamic terms and complete conductance equation. J Chem Soc Earaday Trans 74 1456-1482... 

From equation A2.4.38 we can, finally, deduce Walden s rule, which states that the product of the ionic mobility at infinite dilution and the viscosity of the pure solvent is a constant. In fact... 

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