Dissociation of strong electrolytes

Viewing the dissociation of strong electrolytes another way, we see that the ions formed show little affinity for one another. For example, in HCl in water. Cl has very little affinity for H ... 

A wide variety of data for mean ionic activity coefficients, osmotic coefficients, vapor pressure depression, and vapor-liquid equilibrium of binary and ternary electrolyte systems have been correlated successfully by the local composition model. Some results are shown in Table 1 to Table 10 and Figure 3 to Figure 7. In each case, the chemical equilibrium between the species has been ignored. That is, complete dissociation of strong electrolytes has been assumed. This assumption is not required by the local composition model but has been made here in order to simplify the systems treated. 

Electrical Conductance of Aqueous Solutions of Ammonia and Metal Hydroxides. Check the electrical conductance of 1 W solutions of sodium hydroxide, potassium hydroxide, and ammonia. Record the ammeter readings. Arrange the studied alkalies in a series according to their activity. Acquaint yourself with the degree of dissociation and the dissociation constants of acids and bases (see Appendix 1, Tables 9 and 10). Why is the term apparent degree of dissociation used to characterize the dissociation of strong electrolytes ... 

The form in which chemical analyses of sea water are given records the history of our thought concerning the nature of salt solutions. Early analytical data were reported in terms of individual salts NaCl, CaSO/i, and so forth. After development of the concept of complete dissociation of strong electrolytes, chemical analyses of sea water were given in terms of individual ions Na+, Ca++, Cl-, and so forth, or in terms of known undissociated and partly dissociated species, e.g., HC03 , In recent years there has been an attempt to determine the thermodynamically stable dissolved species in sea water and to evaluate the relative distribution of these species at specified conditions. Table 1 lists the principal dissolved species in sea water deduced from a model of sea water that assumes the dissolved constituents are in homogeneous equilibrium, and (or) in equilibrium, or nearly so, with solid phases. 

From Eqn. (14) it follows that with an exothermic reaction - and this is the case for most reactions in reactive absorption processes - decreases with increasing temperature. The electrolyte solution chemistry involves a variety of chemical reactions in the liquid phase, for example, complete dissociation of strong electrolytes, partial dissociation of weak electrolytes, reactions among ionic species, and complex ion formation. These reactions occur very rapidly, and hence, chemical equilibrium conditions are often assumed. Therefore, for electrolyte systems, chemical equilibrium calculations are of special importance. Concentration or activity-based reaction equilibrium constants as functions of temperature can be found in the literature [50]. 

Strong Electrolytes. Solutes of this type, such as HCl, are completely dissociated in ordinary dilute solutions. However, their colligative properties when interpreted in terms of ideal solutions appear to indicate that the dissociation is a little less than complete. This fact led Arrhenius to postulate that the dissociation of strong electrolytes is indeed incomplete. Subsequently this deviation in colligative behavior has been demonstrated to be an expected consequence of interionic attractions. 

Its dielectric constant, 6.13, is low compared with that of water, 78.3. This low value results in a strong tendency toward incomplete dissociation of strong electrolytes, few of which have dissociation constants as large as 10 Therefore, in the application of the equations in Section 4-5, ion activities can be written simply as concentrations. 

KEN] Kenttamaa, J., A cryoscopic method of studying the incomplete dissociation of strong electrolytes in aqueous solutions, Suom. Kemistil. B, 29B, (1956), 59-64. Cited on pages 181, 182, 183, 187,284,288. 

Ultimately obtaining the desired properties such as density differences and activity coefficients would be complicated, but feasible. This seems not to have been attempted. A much simpler case for complete reactions, such as dissociation of strong electrolytes, is shown in the next section. 

This is the reaction of a weak acid with a strong base. The reaction between an acid and a base always produces water as a product, along with an ionic compound formed from the remaining ions. (This second product is often called a salt.) We can begin by using this idea to write the molecular equation. To generate the ionic equations, then, we account for the dissociation of strong electrolytes into their constituent ions. 

Subsequent theories of non-ideality have been mainly concerned with explaining the concentration and temperature dependences of Y and 0 (3,16). For a comparison with various other theories for the non-ideal part of free energy of solutions, see (14). The interionic attraction theory (3,5,16-18) formulated on the assumption of complete dissociation of strong electrolytes, predicted the InV vs /m linear dependence and explained the Jc dependence of A found empirically by Kohlrausch (3,14) for dilute solutions. Since the square-root laws were found to hold for dilute solutions of many electrolytes in different solvents, the interionic attraction theory gained a wide acceptance. However, as the square root laws were found to be unsatisfactory for concentrations higher than about 0.01m, the equations were extended or modified by the successive additions of more terms, parameters and theories to fit the data for higher concentrations. See e.g., (3,16) for more details. 

Thus, the quantitative correlation of the molal volumes (and hence densities) with oc is in itself a simple and sufficient proof for the correctness of the idea of partial dissociation of strong electrolytes in water. 

Thus, Figures 6 and 7 give further support for the idea of partial dissociation of strong electrolytes. 

Nernst points (5) out that, according to eq. (4a), liquid junction potentials depend only on the ratio of the two osmotic pressures pj and p and not on their absolute values. So if one makes a cell such that in one all the solutions are n times more concentrated than in the other, both must give the same liquid junction potential. Nernst called this the superposition principle and prefaced many of his discussions with it its validity (only approximate, in that osmotic coefficients are ignored) is ix)werful evidence for the complete dissociation of strong electrolytes. 

When ions are dissolved in solution, they dissociate. The Poisson-Boltzmann equation predicts that mobile ions form electrostatic shields around charged objects. Sometimes the dissociation of strong electrolytes is complete. In... 

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