Electrolytes strong, activity coefficients

Studies of the solution properties of heteropoly acids have been somewhat spares despite the general interest in these compounds for many years. Deterents to such studies have been primarily the instability of the compounds and the uncertainty concerning their composition. Conductivity and pH measurements on the heteropoly acids H4[PMonVO40] and H5[PMoi0V2O40] in aqueous solutions and mixed solvents has already been discussed. The acids are strong 1-4 and 1-5 electrolytes, respectively. Activity coefficients of ammonium 6-heteropolymolybdates have been reported and shown these to be 1 3 electrolytes197. ... 

We see from equation (1) that, in very dilute solutions of a strong electrolyte, the activity coefficient is determined only by the concentration and valence of ions, the specific nature of the ions having no appreciable influence. 

Garnsey and Prue made measurements by a heating-curve method on solutions of the perchlorates of lithium and potassium, and of lithium chloride. Measurements were made up to a molality of about 0.25 mol kg . The first two salts behave as strong electrolytes with activity coefficients given by the equation (cf. eqn. 2.9.14)... 

O Connell, J. P., Y. Q. Hu, and K. A. Marshall. 1999. Aqueous strong electrolyte solution activity coefficients and densities from fluctuation solution theory. Fluid Phase Equilibria,... 

The Arrhenius theory of electrolytic solutions was quantitatively restored by explaining the properties of strong electrolytes without activity coefficients on basis of ionic solvation and incomplete dissociation [263-266],... 

Derive the equation of state, that is, the relationship between t and a, of the adsorbed film for the case of a surface active electrolyte. Assume that the activity coefficient for the electrolyte is unity, that the solution is dilute enough so that surface tension is a linear function of the concentration of the electrolyte, and that the electrolyte itself (and not some hydrolyzed form) is the surface-adsorbed species. Do this for the case of a strong 1 1 electrolyte and a strong 1 3 electrolyte. 

The nature of the Debye-Hiickel equation is that the activity coefficient of a salt depends only on the charges and the ionic strength. The effects, at least in the limit of low ionic strengths, are independent of the chemical identities of the constituents. Thus, one could use N(CH3)4C1, FeS04, or any strong electrolyte for this purpose. Actually, the best choices are those that will be inert chemically and least likely to engage in ionic associations. Therefore, monovalent ions are preferred. Anions like CFjSO, CIO, /7-CIC6H4SO3 are usually chosen, accompanied by alkali metal or similar cations. 

Figure 7.4 shows such functions for binary solutions of a number of strong electrolytes and for the purposes of comparison, for solutions of certain nonelectrolytes (/ ). We can see that in electrolyte solutions the values of the activity coefficients vary within much wider limits than in solutions of nonelectrolytes. In dilute electrolyte solutions the values of/+ always decrease with increasing concentration. For... 

They formulated the ionic-strength principle according to which in dilute solutions, the activity coefficient of a given strong electrolyte is the same in all solutions of the same ionic strength. ... 

The beginning of the twentieth century also marked a continuation of studies of the structure and properties of electrolyte solution and of the electrode-electrolyte interface. In 1907, Gilbert Newton Lewis (1875-1946) introduced the notion of thermodynamic activity, which proved to be extremally valuable for the description of properties of solutions of strong electrolytes. In 1923, Peter Debye (1884-1966 Nobel prize, 1936) and Erich Hiickel (1896-1981) developed their theory of strong electrolyte solutions, which for the first time allowed calculation of a hitherto purely empiric parameter—the mean activity coefficients of ions in solutions. 

Lewis and Randall stated that in dilute solutions the activity coefficient of a strong electrolyte is the same in all solutions of the same ionic strength this statement was confirmed in thermodynamic deductions of activity coefficients. The molality version of 7 can be applied in a fully analogous way and allows a more straightforward treatment of solution properties. [Conversion of molality into molarity requires the solution densities e.g., for a solute of molar mass M and a solution of density q we have... 

Because of the electroneutrality condition, the individual ion activities and activity coefficients cannot be measured without additional extrather-modynamic assumptions (Section 1.3). Thus, mean quantities are defined for dissolved electrolytes, for all concentration scales. E.g., for a solution of a single strong binary electrolyte as... 

Van t Hoff introduced the correction factor i for electrolyte solutions the measured quantity (e.g. the osmotic pressure, Jt) must be divided by this factor to obtain agreement with the theory of dilute solutions of nonelectrolytes (jt/i = RTc). For the dilute solutions of some electrolytes (now called strong), this factor approaches small integers. Thus, for a dilute sodium chloride solution with concentration c, an osmotic pressure of 2RTc was always measured, which could readily be explained by the fact that the solution, in fact, actually contains twice the number of species corresponding to concentration c calculated in the usual manner from the weighed amount of substance dissolved in the solution. Small deviations from integral numbers were attributed to experimental errors (they are now attributed to the effect of the activity coefficient). 

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. 

Meissner, H. P. and C. L. Kusik, "Activity Coefficients of Strong Electrolytes in Multicomponent Aqueous Solutions," AIChE J., 1972, 18, 294. 

Pitzer, K. S. and Guillermo Mayorga, "Thermodynamics of Electrolytes. II. Activity and Osmotic Coefficients for Strong Electrolytes with One or Both Ions Univalent," J. Phys. Chem., 1973, 77, 2300. 

Meissner, H.P. "Prediction of Activity Coefficients of Strong Electrolytes in Aqueous Systems," paper presented at symposium on "Thermodynamics of Aqueous Systems with Industrial Application," Washington, D.C., October 22-25,... 

As can be seen less than 2% error in this multicomponent system occurred when using ECES. This system is quite different than the NH3-CO2-H2O system since we are dealing only with strong electrolytes. For example, the second datum point predicted by ECES give the following results for the concentrations, activity coefficients and water activity in the aqueous phase. 

Hamer, W. J. "Theoretical Mean Activity Coefficients of Strong Electrolytes in Aqueous Solution from 0 to 100 C" NSRDS-NBS 24, U.S. Department of Commerce, National Bureau of Standards, December 1968. 

Prediction of Activity Coefficients of Strong Electrolytes in Aqueous Systems... 

Most hydrometallurgical systems operate in the 50°C to 250°C temperature range and can be classified as strong electrolytes with ionic strengths ranging from 0.1m to 6m or higher. Furthermore, experimental data are seldom available in the regions of interest. Consequently, the successful use of thermodynamics requires that extrapolations be made in temperature, and that estimates be made of ionic activity coefficients. 

ACTIVITY, ACTIVITY COEFFICIENTS, AND OSMOTIC COEFFICIENTS OF STRONG ELECTROLYTES... 

ACTIVITY COEFFICIENTS OF SOME STRONG ELECTROLYTES Experimental Values... 

With the experimental methods described, as well as with several others, the activity coefficients of numerous strong electrolytes of various valence types have been calculated. Many of these data have been assembled and examined critically by Harned and Owen [2], More recent evaluations for uni-univalent electrolytes have been made by Hamer and Wu [6], and for uni-bivalent electrolytes by Goldberg [7], Data used by the authors in Refs. 6 and 7 are fitted to an expression of the form... 

Raji Heyrovska [18] has developed a model based on incomplete dissociation, Bjermm s theory of ion-pair formation, and hydration numbers that she has found fits the data for NaCl solutions from infinite dilution to saturation, as well as several other strong electrolytes. She describes the use of activity coefficients and extensions of the Debye-Hiickel theory as best-fitting parameters rather than as explaining the significance of the observed results. ... 

We dehned the activity coefficient for strong electrolytes in Chapter 19 in Equations (19.9) and (19.24) as... 

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