True electrolytes

Trouton s rule phys chem An approximation rule for the derivation of molar heats of vaporization of normal liquids at their boiling points. traCit anz. riil ) true condensing point See critical condensation temperature. trii kan dens ir). point) true electrolyte puys chem A substance in the solid state that consists entirely of ions. trir i lek-tr9,lTt)... 

In the pure state, a potential electrolyte such as oxalic acid (HOOCCOOH) consists of uncharged molecules. A true electrolyte such as NaCl in the pure state consists of two separate ions, Na and CP. The proton is a bare nucleus it has no electrons. It is chemically unstable as an isolated entity because of its affinity for electrons. As a result, the proton reacts with the free electron pair of oxygen in the H2O molecule. 

Electrolyte — Compounds that dissociate (- dissociation) into -> ions upon dissolution in -> solvents or/and upon melting and which provide by this the - ionic conductivity. Also, compounds that possess in the solid state a rather high ionic conductivity are called - solid electrolytes. - True electrolytes are those which are build up of ions in the solid state (or pure form), whereas potential electrolytes are those which form ions only... 

Such ionic crystals are known as true electrolytes or ionophores (the Greek suffix phore means bearer of thus, an ionophore is a substance that bears ions ). When a true electrolyte is melted, its ionic lattice is dismantled and the pure liquid true electrolyte shows considerable ionic conduction (Chapter 2). Thus, the characteristic of a true electrolyte is that in the pure liquid form it is an ionic conductor. All salts belong to this class. Sodium chloride therefore is a typical true electrolyte. 

Now, the first requirement of an electrolyte is that it should give rise to a conducting solution. From this point of view, it appears that acetic acid will never answer the requirements of an electrolyte it is nomomc. When, however, acetic add is dissolved in water, an interesting phenomenon oeeurs ions are produced, and therefore the solutions conduct electricity. Thus, acetic acid, too, is a type of eleetrolyte it is not a true electrolyte, but a potential one ( one which can, but has not yet, become ). Potential electrolytes are also called ionogens, i.e., ion producers. ... 

Fig. 3.1. Schematic diagnam to illustrate the difference in the way potential electrolytes and true electrolytes dissolve to give ionb solutions (a) Oxalic acid (a potential electrolyte) undergoes a proton-transfer chemical reaction with waterto give rise to hydrogen ions and oxalate ions, (b) Sodium chloride (a true electrolyte) dissolves by the solvation of the Na and Cl bns in the crystal.

The result of the proton transfer is that two ions have been produced (1) an acetate ion and (2) a hydrated proton. Thus, potential electrolytes (organic acids and most bases) dissociate into ions by ionogenic, or ion-forming, chemical reactions with solvent molecules, in contrast to true electrolytes, which often give rise to ionic solutions by physical interactions between ions present in the ionic crystal and solvent molecules (Fig. 3.1). 

The classification into trae and potential electrolytes is a modem one. It is based on a knowledge of the structure of the electrolyte whether in the pure form it consists of an ionic lattice (true electrolytes) or neutral molecules (potential electrolytes) (Fig. 3.2). It is not based on the behavior of the solute in any particular solvent. 

Fig. 3.2. Electrolytes can be classified as (a) potential electrolytes (e.g., oxalic add), which in the pure state consist of uncharged molecules, and (b) true electrolytes (e.g., sodium chloride), which in the pure state consist of ions.

In contrast, true electrolytes are completely dissociated into ions when the parent salts are dissolved in water. The resulting solutions generally consist only of solvated ions and solvent molecules. The dependence of many of their properties on concentration (and therefore mean distance apart of the ions in the solution) is determined by the interactions between ions. To understand these properties, one must understand ion-ion interactions. 

The Debye-Hiickel approach is an excellent example of electrochemical theory. Electrostatics is introduced into the problem in the form of Poisson s equation, and the chemistry is contained in the Boltzmann distribution law and the concept of true electrolytes (Section 3.2). The union of the electrostatic and chemical modes of... 

This equation indicates how the activity coefficient depends on the extent of ion association. In fact, this equation constitutes the bridge between the treatment of solutions of true electrolytes and that of solutions of potential electrolytes. 

The interaction of an ion in solution with its environment of solvent molecules and other ions has been the subject of the previous two chapters. Now, attention will be focused on the motion of ions through their environment. The treatment is restricted to solutions of true electrolytes. 

Apart from improvements made by taking into account the fact that ions do indeed take up some of the space in electrolytic solutions, one has to consider also that ion association occurs in true electrolytes. 

Not only is water the most plentiful solvent, it is also a most successful and useful solvent. There are several facts that support this description. First, the dissolution of true electtolytes occurs by solvation (Chapter 2) and therefore depends on the free energy of solvation. A sizable fraction of this free energy depends on electrostatic forces. It follows that the greater the dielectric constant of the solvent, the greater is its ability to dissolve true electrolytes. Since water has a particularly high dielectric constant (Table 4.23), it is a successful solvent for true electrolytes. 

A nonaqueous solution must be able to conduct electricity if it is going to be useful. What determines the conductivity of a nonaqueous solution Here, the theoretieal principles involved in the conductance behavior of true electrolytes in nonaqueous solvents will be sketched. However, before that, let the pluses and minuses of working with nonaqueous solutions (particularly those involving organic solvents) be laid out. 

When one switches from water to some nonaqueous solvent, the magnitudes of several quantities in the Debye-Hiickel-Onsager equation alter, sometimes drastically, even if one considers the same true electrolyte in aU these solvents. These quantities are the viscosity and the dielectric constant of the medium, and the distance of closest approach of the solvated ions (i.e., the sum of the radii of the solvated ions). As a result, the mobilities of the ions at infinite dilution, the slope of the A versus... 

Some Conclusions about the Conductance of Nonaqueous Solutions of True Electrolytes... 

The change from aqueous to nonaqueous solutions of true electrolytes results in characteristic effects on the conductance. The order of magnitude of the equivalent conductivity at infinite dilution is approximately the same in both types of solutions and is largely dependent on the viscosity of the solvent. However, the slope... 

Thus, nonaqueous solutions of true electrolytes are not to be regarded with unrestrained optimism for applications in which there is a premium on high specific conductivity and minimum power losses through resistance heating. One may have to think of solutions of potential electrolytes where there is an ion-forming reaction between the electrolyte and the solvent (Section 2.4). 

A.22.5 When melted, a true electrolyte is a liquid ionic conductor, and it can create a liquid ionic conductor when dissolved in solvent. A potential electrolyte must interact with a solvent, e.g. water, to create a liquid ionic conductor it does not form one on its own even when melted. 

Tetraalkylammonium chlorides, their melting True electrolytes... 

In aprotic solvents, such as acetonitrile (H3CCN), dimethyl sulfoxide (H3CSOCH3), or methylisobutyl ketone (H3CCOCH(CH3)2), the potential electrolytes can be dissolved, but not ionized. These solvents have moderate permittivity, and they support the dissociation of true electrolytes. Dissolved acids (e.g., C6H5OH or H2O) may act as proton donors if a certain proton acceptor is created in the electrode reaction. 

NaCI dissolved in water is the true electrolyte, and the Na and Cl are split and free. Even if NaCI is the true electrolyte, the whole electrolyte solution is often also called just the electrolyte. 

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