Activity coefficients of electrolytes

In view of the electrostatic nature of forces that primarily lead to deviation of the behaviour of electrolyte solutions from the ideal, the activity coefficient of electrolytes must depend on the electric charge of all the ions present. G. N. Lewis, M. Randall and J. N. Br0nsted found experimentally that this dependence for dilute solutions is described quite adequately by the relationship... 

The Davies equation [29] has been used extensively to calculate activity coefficients of electrolytes at fairly low ionic strengths. 

I. 46. The magnitude of the coefficient reflects the electric charge distribution of the ionic species. A 0.1 molal solution of Al2(S04)3 has an activity coefficient of only 0.035. It should also be noted that, in dilute solutions, activity coefficients of electrolytes decrease in magnitude with increasing concentration. A minimum is reached and the coefficient then increases with concentration. See Activity Debye-Huckel Law Biomineralization... 

Mean activity coefficient of electrolyte B in solution is given by... 

Debye and Hiickel (1923) used a similar approach to Gouy and Chapman to calculate the activity coefficients of electrolytes. 

Activity Coefficients of Uni-Univalent Chlorides. The second application is to the activity coefficients of electrolytes as a function of the dielectric constant of the media. Returning to Equation 32, for electrolytes at infinite dilution only the Born term remains, that is,... 

Activity Coefficients of Electrolytes in Water-Polyethylene Glycol Mixed Solvent by Isopiestic Method... 

R. S. Treptow, The Lead-Acid Battery Its Voltage in Theory and Practice, J. Chem. Ed. 2002, 79, 334. Includes activity coefficients of electrolyte in the battery. 

Just as we discussed in Chapter 9, we can use measured activities of solvents (determined from vapor pressure, freezing-point depression, boiling-point elevation, or osmotic pressure) to determine activity coefficients of electrolytes in solution. For an ionic substance, the Gibbs-Duhem equation is... 

As can be seen from these equations the specific nature of individual ions is not expressed any more in very diluted solutions and the activity coefficient is determined solely by the ionic strength and the valence type of the electrolyte. Assuming the solutions to be properly diluted, the activity coefficients of electrolytes of the same valence type are identical in all solutions of the same ionic strength. 

The -> concentration cells are used only for determination of -> transport (transference) numbers, - activity, and -> activity coefficients of electrolytes and other quantities. Their practical application is limited by the -> selfdischarge due to the spontaneous diffusion process. In concentration cells no chemical reactions occur, a physical process (the equalization of activities by diffusion) causes the potential difference and supplies the energy. 

Values of Activity Coefficients.—Without entering into details, it is evident from the foregoing discussion that activities and activity coefficients are related to chemical potentials or free energies several methods, both direct and indirect, are available for determining the requisite differences of free energy so that activities, relative to the specified standard states, can be evaluated. In the study of the activity coefficients of electrolytes the procedures generally employed are based on measurements of either vapor pressure, freezing point, solubility or electromotive force. The results obtained by the various methods arc... 

TABLE XXXIV. MEAN ACTIVITY COEFFICIENTS OF ELECTROLYTES IN AQUEOUS... 

Fiq. 46. Activity coefficients of electrolytes of different valence types... 

Individual Ion Activities.—The methods described in Chap. V for the determination of the activities or activity coefficients of electrolytes, e well as those depending on vapor pressure, freezing-point or other osmotic measurements, give the nean values for b >th ions into which the solute A convenient form of this equat ion for approximate purposes is... 

Corresponding to each chemical potential there is an activity coefficient defined in terms of equation (20.4). By convention, the activity coefficients of electrolytes are always expressed in terms of the ideal dilute solution as standard reference state, cf. chap. XXI, 3. Thus in the case of an aqueous NaCl solution we may write... 

In discussing the relation between the activity coefficients of electrolytes and the concentration of the 4 90 solution, use is made of the ionic strength, defined by... 

For 0.005 m KfSO4 solution at 25° C. Calculated mean activity coefficient of electrolyte using Debye-Huckel limiting law (Debye Huckel constant A at 25° C is 0.509 kg1/2 moL1/2) ... 

Amalgam Cells. F6r the determination of activity coefficients of electrolytes the method depending upon the measurement of the potentials of concentration cells without transference has already been discussed in Chapter 6. Two examples of such cells were mentioned. These were the following ... 

Potentiometry may also be used to determine activity coefficients of electrolytes the measured e.m.f. of an electrochemical cell is related to the activities of the ions. These measurements can yield very accurate values near room temperature for systems where reversible and reproducible electrodes have been developed. Potentiometry at high temperatures is much more difficult this is an area of active research. 

The mean activity coefficient of electrolyte A (assumed to be completely dissociated) is... 

In 1923 Peter Debye and Erich HUckel published two remarkable papers that described an a priori method of calculating the activity coefficient of electrolytic solutes in dilute solution. Without doubt this was one of the major breakthroughs in electrolyte solution theory. 

Many different techniques can be used to measure activity coefficients of electrolytic solutes, many of which are electrochemical. Most of these methods are reviewed in standard references (e.g., Harned and Owen, 1958 Monk, 1961 Robinson and Stokes, 1968, Ch. 8). Solutions of geological interest can span considerable temperature ranges, and it has often proven simplest experimentally to measure the activity of the... 

Mean Activity Coefficients of Electrolytes as a Fiuiction of Concentration... 

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