Dissociation of electrolyte

Debye-Huckel theory assumes complete dissociation of electrolytes into solvated ions, and attributes ionic atmosphere formation to long-range physical forces of electrostatic attraction. The theory is adequate for describing the behaviour of strong 1 1 electrolytes in dilute aqueous solution but breaks down at higher concentrations. This is due to a chemical effect, namely that short-range electrostatic attraction occurs... 

It was found in later work that it is precisely the idea of ionic hydration that is able to explain the physical nature of electrolytic dissociation. The energy of interaction between the solvent molecules and the ions that are formed is high enough to break up the lattices of ionophors or the chemical bonds in ionogens (for more details, see Section 7.2). The significance of ionic hydration for the dissociation of electrolytes had first been pointed out by Ivan A. Kablukov in 1891. 

Bosch, Roses and coworkers62 65 66 have used the dissociation of electrolytes in binary solvents of low permittivity using 2-methylpropanol or propan-2-ol as the main solvent... 

The dissolved state of the electrolytes in water has long been of great interest. More than a century ago, Mendelejew [12] suggested that sulphuric acid forms hydrates, and Arrhenius [13] put forward the theory of partial dissociation of electrolytes, both in the same Jorrmal. These pioneering ideas have eventually proved to be correct [14] for electrolyte solutions from zero to saturation. 

Thus far, we have not introduced any assumptions about the dissociation of electrolytes in order to describe their experimental behavior. As far as thermodynamics is concerned, such details need not be considered. We can take the limiting law in the form of Equation (19.1) as an experimental fact and derive thermodynamic relationships from it. Nevertheless, in view of the general applicability of the ionic theory, it is desirable to relate our results to that theory. 

Solvent effects in electrochemistry are relevant to those solvents that permit at least some ionic dissociation of electrolytes, hence conductivities and electrode reactions. Certain electrolytes, such as tetraalkylammonium salts with large hydrophobic anions, can be dissolved in non-polar solvents, but they are hardly dissociated to ions in the solution. In solvents with relative permittivities (see Table 3.5) s < 10 little ionic dissociation takes place and ions tend to pair to neutral species, whereas in solvents with 8 > 30 little ion pairing occurs, and electrolytes, at least those with univalent cations and anions, are dissociated to a large or full extent. The Bjerrum theory of ion association, that considers the solvent surrounding an ion as a continuum characterized by its relative permittivity, can be invoked for this purpose. It considers ions to be paired and not contributing to conductivity and to effects of charges on thermodynamic properties even when separated by one or several solvent molecules, provided that the mutual electrostatic interaction energy is < 2 kBT. For ions with a diameter of a nm, the parameter b is of prime importance ... 

We will see in Chapter 10, when we deal with the dissociation of electrolytes into ions, that, in general, the chemical potential of a dissociating solute is the chemical potential of its component parts, whereas the activity of the solute is the product of the component parts. 

Feb. 19,1859, Wijk, Sweden - Oct. 2,1927, Stockholm, Sweden). Arrhenius developed the theory of dissociation of electrolytes in solutions that was first formulated in his Ph.D. thesis in 1884 Recherches sur la conductibilit galvanique des dectrolytes (Investigations on the galvanic conductivity of electrolytes). The novelty of this theory was based on the assumption that some molecules can be split into ions in aqueous solutions. The - conductivity of the electrolyte solutions was explained by their ionic composition. In an extension of his ionic theory of electrolytes, Arrhenius proposed definitions for acids and bases as compounds that generate hydrogen ions and hydroxyl ions upon dissociation, respectively (- acid-base theories). For the theory of electrolytes Arrhenius was awarded the Nobel Prize for Chemistry in 1903 [i, ii]. He has popularized the theory of electrolyte dissociation with his textbook on electrochemistry [iv]. Arrhenius worked in the laboratories of -> Boltzmann, L.E., -> Kohlrausch, F.W.G.,- Ostwald, F.W. [v]. See also -> Arrhenius equation. 

Table 1.2 Degree of dissociation of electrolytes, calculated from freezing point and conductivity measurements...

Table 1.3 Degree of dissociation of electrolytes in O 1m aqueous solutions...

The most elaborate treatment of the dissociation of electrolytes in solutions is the one given by Fuoss and Onsager (9, 10). The so-called F.O. equation, applied to I-I associated electrolytes is... 

Mtributed to the absence of the necessary experimental work for 0-5-2 normal solutions of non-electrolytes, that is, of systematic determinations of all the quantities which appear in the equations (namely, concentration by weight and by volume, heat of dilution, etc.). The theoretical interpretation of the data for solutions of electrolytes must be postponed until the behaviour of non-electrolytes has been explained. The dissociation of electrolytes introduces a new complication which cannot be treated with success until the osmotic pressure laws for concentrated solutions have been elucidated. 

Additives will influence solute-solvent interfacial energies or dissociation of electrolytes through changes in dielectric constant. A reduction in ionisation through a decrease in dielectric constant will favour decreased solubility, but this effect may be counterbalanced by the greater affinity of the undissociated species in the presence of the cosolvent. 

Colligative Properties and Dissociation of Electrolytes 14-15 Osmotic Pressure... 

In electrolyte solutions, the interaction between ions leads to the formation of ion pairs. The van t Hoff factor provides a measure of the exteut of dissociation of electrolytes in solution. 

Experiment 52. The Determination of the Degree of Dissociation of Electrolytes from the Freezing Point of Solutions. 

On the other hand solute relaxation measurements are sensitive to changes in the environment, and in principle afford information about the dissociation of electrolytes. They have not been used, however, to calculate dissociation constants of acids or bases, because of the complexity of the treatment required. 

We would finally make a few remarks on the double layer at the interface of two liquids. Except when at least one of the liquids is non-polar, and the solubility or electrolytic dissociation of electrolytes, accordingly, zero, electrolytes added to the system, even in very small amounts, will each act there as... 

In principle, the dissociation of electrolytes obeys to the law of mass actions as described in Chapter 12 for conventional chemical reactions. For evaluation, the Gibbs energies of formation of the compounds involved are needed. For some of the most important electrolyte compounds, they are listed in Appendix D. 

As has been pointed out, the equations are all integrations of the Gibbs-Duhem relationship. They consequently cannot be applied to systems which when treated in the ordinary fashion apparently do not follow this basic relation, as in the case of dissociation of electrolytes in solution. 

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