Electrolytes, activity coefficients

Rard also employed Pitzer s electrolyte activity coefficient model to correlate the data. It was found that the quality of the fit depended on the range of molalities that were used. In particular, the fit was very good when the molalities were less than 3 mol/kg. 

Estimate Pitzer s electrolyte activity coefficient model by minimizing the objective function given by Equation 15.1 and using the following osmotic coefficient data from Rard (1992) given in Table 15.5. First, use the data for molalities less than 3 mol/kg and then all the data together. Compare your estimated values with those reported by Rard (1992). Use a constant value for in Equation 15.1. 

Thiessen, D.B., and Wilson, "An Isopiestic method for Measurement of Electrolyte Activity Coefficients", AIChE J., 33(11), 1926-1929, 1987. 

A very fine example was provided by the extensive use of Professor Pitzer s electrolyte activity coefficient theory within several acid gas phase equilibrium models. 

The success of Harned s rule for ternary solutions is largely fortuitous, and the rule has no theoretical basis to expect that it would be useful for solutions containing more than two electrolytes. Furthermore, for high concentrations of several electrolytes, activity coefficients such as Y3(g are hypothetical. There are, unfortunately, few experimental data available to test Harned s rule for concentrated solutions of three or more electrolytes. 

A unitless correction factor that relates the relative activity of a substance to the quantity of the substance in a mixture. Activity coefficients are frequently determined by emf (electromotive force) or freezing-point depression measurements. At infinite dilution, the activity coefficient equals 1.00. Activity coefficients for electrolytes can vary significantly depending upon the concentration of the electrolyte. Activity coefficients can exceed values of 1.00. For example, a 4.0 molal HCl solution has a coefficient of 1.76 and a 4.0 molal Li Cl has a value of... 

Gordon, J. E., and R. L. Thorne, Salt effects on non-electrolyte activity coefficients in mixed aqueous electrolyte solutions. II. Artificial and natural sea waters , Geochim. Cosmochim. Acta, 31, 2433-2443 (1967b). 

KUS/MEI] Kusik, C. L., Meissner, H. P., Electrolyte activity coefficients in inorganic processing, AlChE Symp. Sen, 74, (1978), 14-20. Cited on page 571. 

Use of Pitzer s Equations to Estimate Strong-Electrolyte Activity Coefficients in Aqueous Flue Gas Desulfurization Processes... 

Pitzer s formulation offers a satisfactory and desirable way to model strong electrolyte activity coefficients in concentrated and complex mixtures. When sufficient experimental data are available, one can make calculations which are considerably more accurate than those presented in this paper. Attaining high accuracy requires not only experimentally-based parameters but also that one employ third virial coefficients and additional mixing terms and include explicit temperature dependencies for the various parameters. 

In this section we discuss certain characteristics of electrolyte solutions and present equations for the prediction or correlation of electrolyte activity coefficients in solution. Since the derivations of these equations are complicated and beyond the scope of this book, they are not given. 

The strongly hydrophyllic nature of the exchanger and the resulting constancy of the internal environment permit assessment of electrolyte activity coefficient ratios in the external mixed solvent through the equation... 

Reproduced by permission of the American Institute of Chemical Engineers "Electrolyte Activity Coefficients in Inorganic ProcessingKusik, C.L. and H.P. Meissner, AIChE Symp. Ser. 74(173), p. 17 (1978). 

M7. Meissner, H.P. and C.L. Kusik, "Electrolyte Activity Coefficients in Inorganic Processing", AIChE Symposium Series 173, 74, 14 (1978)... 

OP3t Rosenblatt, G., "Use of Pitzer s Equations to Estimate Strong-Electrolyte Activity Coefficients in Aqueous Flue Gas Desulfurization Processes", Flue Gas Desulfurization. J.L. Hudson and G.T. Rochelle, eds., ACS Symposium Series 188, p57 (1982)... 

Some of the electrolytes to be tested precipitate in hydrated forms at 25 C. It is therefore necessary to calculate the water activities in addition to the electrolyte activity coefficients in order to model the solutions. The water activity may be calculated using an equation presented specifically for it s calculation, or from the results of an osmotic coefficient equation. 

A Nernst equation may be written for every galvanic cell at equilibrium. Therefore the equation is the basis of all thermodynamic applications of potentiometry (i.e. measurement of open-circuit cell potentials by means of a potentiometer or other zero-current device). Cells may be constructed and appropriate Nernst equations written to find, for example, the dissociation constant of water, and many electrolyte activity coefficients and stability and solubilit,v constants. Potentiometric titration curves are also interpieted by means of the appropriate Nernst equation. 

Here the thermodynamic factor relates to the derivative of the electrolyte activity coefficient with respect to molality m through... 

Fawcett WR, Tikanen AC (1996) Role of solvent permittivity in estimation of electrolyte activity coefficients on the basis of the mean spherical approximation. J Phys Chem 100 4251-4255... 

Electrolyte Activity coefficient-sEq. (2.1) [2]c<1.0m Kielland[7] Marcus [8] Marcus [8] Molecular mechanics... 

The Debye-Hiickel theory provides an accurate limiting law for the activity coefficients of electrolyte solutes. A semi-empirical equation, the Davies equation, can provide usable estimates of electrolyte activity coefficients at larger concentrations. 

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