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Strongly associated electrolytes

Since each of the theoretical treatments described in sect. 5.2.2 gives different values for and J2, it is obvious that the numerical value obtained for will depend to some extent on the particular theory employed. This effect is larger with smaller association constants because then the J terms in eqn. 5.3.4 are large compared to the last term. On the other hand, when is about 10 mol 1, the number of free ions per unit volume is small (for c = 0.01 molar, the concentration of free ions is about 4.10" molar) so that the last term in eqn. 5.3.4 is the dominant one. In this case the theoretical form of the concentration dependence of the conductance is far less important and is little dependent on it. Hence simpler equations are employed to deal with these strongly associated electrolytes. [Pg.563]

Special problems are encountered in strongly associated electrolytes where A changes very steeply with c and the Debye-Hiickel-Onsager effects play a minor role. From several simpler equations the most widely used is that proposed by Sheldovsky... [Pg.29]

Conductance reflects the concentration of ions in the solution, not of neutral molecules. It is therefore a suitable method for determining the equilibrium constants of both strong and weak electrolytes. These determinations are based on Eqs. (44) and (46) and on other relationships not given here. Equation (46) is especially suitable for strongly associated electrolytes where the interactions between the ions are small and the resulting values of and Ka are reasonably accurate. The dissociation of water, alcohols, etc., as well as the solubility product can be estimated on the basis of conductance. A more complicated approach must be taken for cases where the solvent itself is strongly dissociated. [Pg.32]

Krienke H, Barthel J, Holovko MF, Protsykevich I, Kalyushnyi Y (2000) Osmotic and activity coefficients of strongly associated electrolytes over large concentration ranges from chemical model calculations. J Mol Liquids 87 191... [Pg.1392]

Positive deviations to the DHLL are observed for strongly associated electrolytes as MgS04 at moderate temperatures or NaCl close to the water critical temperature. The reason of the deviation is the reduction of the electrostrictive effect when ion-pairs are formed, which leads to an expansion of the solution. [Pg.142]

For weakly and moderately associated electrolytes, 10< (A<104, no problem generally occurs in obtaining reliable values for KA and A0 from conductivity measurements. Strong association, however, as known for many salts in the solvent class 6, often entails unrealistic A ... [Pg.467]

Here we discuss a thermodynamic model appropriate to describe effects of strong association in dilute solutions. To have a definite example, consider a dilute electrolyte solution of a salt, say M X, that in solution dissociates to produce cations M of charge qu e and anions X of charge —qx e with aq [ = bqx- The interactions between these ions are composed of short-ranged interactions and long-ranged ionic interactions screened by the dielectric response of the solvent with dielectric constant e, as with r the distance between the ions. If the... [Pg.94]

Figure 7 shows the concentration of fixed ions of Nafion. The concentration of fixed ions increases drastically with electrolyte concentration because of the ion-cluster morphology and the highly dehydrated state of the membrane in concentrated electrolytes, as well as the mass-action effect in counterion activity. Kimoto has recently shown that in concentrated alkaline solutions the effective concentration of fixed ions is less than half of the value calculated from Eq. (8). This decrease is due to the ion-pair formation and strong association in the ion cluster. [Pg.457]

Extended laws are available for the variation with concentration of the transport coefficients of strong and associated electrolyte solutions at moderate to high concentrations. Like the CM calculations, this work is based on the Fuoss-Onsager transport theory. The use of MSA pair distribution functions leads to analytical expressions. Ion association can be introduced with the help of the chemical method. A simplified version of the equations, by taking average ionic diameters, reduces the complexity of the original formulas without really reducing the accuracy of the description and is therefore recommendable for practical use for up to 1-M solutions. [Pg.116]

The point is that it is risky to draw conclusions about the details of chemical reactions on the basis of volumetric data alone, or in fact of any indirect evidence. This point will become important when we discuss the two main interpretations of electrolyte association in Chapter 15. Nevertheless, many substances do show weak to strong association into clusters, and this chemical interpretation of gas nonideality is explored extensively in Prausnitz et al. (1999, 5.8). [Pg.383]

The evolution of the hydrodynamic diameter and absolute scattering intensity with the solution pH shows the expected behavior for this specific PIC. Indeed, when the solution pH is set between 5 and 7, both PMAA and PEI (or chitosan) exist in their ionized form since the pKa of PMAA = 5.5, pKb of PEI = 7-9 (pKb of chitosan = 6.5) [16]. Therefore all the negative and positive sites on the poly electrolyte backbone are accessible in this pH range. When PMAA and PEI are mixed together there is complete and strong association of the two polyelectrolytes due to charge neutralization. The formation of the electrostatic complex triggered by the pH yields PIC micelles with a finite size and stabilized by a corona of PEO chains in water. [Pg.175]

Mixtures of strong and associating electrolytes have been described also [36, 38]. For mixed electrolytes a natural extension of eqs 5.38 and 5.39 is... [Pg.108]

For weakly and moderately associated electrolytes, 10 < Ka < lO, generally no problem occurs in obtaining reliable values for Ka and Aq from conductivity measurements. However, strong association, as known for many salts in the solvent class 6, often entails unrealistic Ao-values and Ka-values. This is a problem of data analysis caused by the large extrapolation of very small Ai-values at the lowest concentration of a ran when compared with the expected Ao-value. Improved estimates for Ao are obtained with the help of the Walden rule at constant temperature T, if Ao is known for the electrolyte in another solvent (2) where a small association constant does not prohibit its determination, and rj is known for both solvents (1, 2). [Pg.553]

However, it should be stressed that battery electrolytes are often strongly associated. Therefore the results of this method for battery electrolytes should be used with caution. Perhaps, by comparing results for model systems including conductivity measurements, it wiU be possible to gain a correct interpretation of values determined with this method. [Pg.605]

Another circumstance which complicates the analysis of kinetics of reactions in nonaqueous solutions is worth noting. Most solvents have low dielectric constants, and this results in an incomplete dissociation of electrolytes (or a strong association of ions). Consequently, we get a set of different reacting particles, and the dependence of the rate of the process on concentration becomes more complicated. These effects are manifested most markedly in the case of a strong specific adsorption of the associate. In this case the associates play an active role even in aqueous solutions. For example, as was mentioned in section 2.2, the discharge of HI in aqueous solution for a mean ionic molarity 2.1 M for HI was observed, while in ethylene glycol the onset of HI discharge is observed already at - 0.3 M. The reduction of persulfate is... [Pg.236]

The term electrochromism was apparently coined to describe absorption line shifts induced in dyes by strong electric fields (1). This definition of electrocbromism does not, however, fit within the modem sense of the word. Electrochromism is a reversible and visible change in transmittance and/or reflectance that is associated with an electrochemicaHy induced oxidation—reduction reaction. This optical change is effected by a small electric current at low d-c potential. The potential is usually on the order of 1 V, and the electrochromic material sometimes exhibits good open-circuit memory. Unlike the well-known electrolytic coloration in alkaU haUde crystals, the electrochromic optical density change is often appreciable at ordinary temperatures. [Pg.156]

Because the film growth rate depends so strongly on the electric field across it (equation 1.115), separation of the anodic and cathodic sites for metals in open circuit is of little consequence, provided film growth is the exclusive reaction. Thus if one site is anodic, and an adjacent site cathodic, film thickening on the anodic site itself causes the two sites to swap roles so that the film on the former cathodic site also thickens correspondingly. Thus the anodic and cathodic sites of the stably passive metal dance over the surface. If however, permanent separation of sites can occur, as for example, where the anodic site has restricted access to the cathodic component in the electrolyte (as in crevice), then breakdown of passivity and associated corrosion can follow. [Pg.131]

A criterion for the presence of associated ion pairs was suggested by Bjerrum. This at first appeared to be somewhat arbitrary. An investigation by Fuoss,2 however, threw light on the details of the problem and set up a criterion that was the same as that suggested by Bjerrum. According to this criterion, atomic ions and small molecular ions will not behave as strong electrolytes in any solvent that has a dielectric constant less than about 40. Furthermore, di-divalent solutes will not behave as strong electrolytes even in aqueous solution.2 Both these predictions are borne out by the experimental data. [Pg.64]

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... [Pg.485]


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Associated electrolytes

Strong electrolytes

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