GUNTELBERG equation

Siveral approaches are available in the case of mixed electrolyte solutions. The Guntelberg equation can be used at very high dilutions to avoid the ambiguity in the meaning of aD, the distance of closest approach, when several electrolytes are present. This equation is empirical and has fewer terms than the Debye-Huckel extended equation. I found it to yield poor agreement with experimental results even at m = 0.01 for NaCl at 25°C (y+ caic = 0.8985 and y+ exp = 0.9024). For the Davies equation for m = 0.20 one obtains y+ calc = 0.752 andy+exo = 0.735 also for NaCl at 25°C. 

Green RW and Tong HK, The constitution of the pyridine monocarboxylic acids in their isoelectric forms, JACS, 78,4896-4900 (1956). Used a glass electrode standardized with phflialate solution (pH = 4.00) and the Guntelberg equation to correct for I. Estimated the microconstants from spectrophotometric data on the acid and its methyl ester pJ A, 2.11 pK, 3.13 pJ o 4.77 pKo, 3.75 where the subscripts represent the following equilibria A, diprotonated to zwitterion B, diprotonated to neutral C, zwitterion to fully deprotonated D, neutral to fully deprotonated. Also reported the corresponding data for picolinic and isonicotinic acids. 

The Debye-Hiickel limiting law (equation 3.32) has to be modified for all but the most dilute solutions, and many modifications have been proposed. For example, the Guntelberg equation ... 

The only three methods which do not require curve-fitting at present are the use of the Debye-Huckel limiting law and of the equations of Guntelberg and of Davies. Unfortunately these equations are of value only in very dilute and simple solutions. 

Guntelberg proposed a simple equation for the hydrated ion size by assuming BRmin = 1, since ions are approximately 1 A and B is on the order of 10s cm... 

It should be noted that, for solutions of ionic strength < 10 mol L , either Equation (3.4) or the Giintelberg approximation (3.5), which incorporates an average value of 3 for ai, can be used. The Guntelberg approximation is particularly useful in calculations where a number of ions are present in solution or when values of the ion size parameter are poorly defined. 

Describe the difference between the Guntelberg and Debye charging processes. Which process should be more effective in deriving an equation for the activity coefficient ... 

In dilute solutions (/ < 10 M), that is, in fresh waters, our calculations are usually based on the infinite dilution activity convention and thermodynamic constants. In these dilute electrolyte mixtures, deviations from ideal behavior are primarily caused by long-range electrostatic interactions. The Debye-Huckel equation or one of its extended forms (see Table 3.3) is assumed to give an adequate description of these interactions and to define the properties of the ions. Correspondingly, individual ion activities are estimated by means of individual ion activity coefficients calculated with the help of the Guntelberg or Davies (equations 3 and 4 of Table 3.3) or it is often more convenient to calculate, with these activity coefficients, a concentration equilibrium constant valid at a given /,... 

A similar equation has been proposed by Guntelberg in which Ba = 1, which corresponds to a value of a = 0.304 nm ... 

Figures 4.3 and 4.4 show the mean activity coefficients of NaCl at 25°C calculated with the equations of GUntelberg, Guggenheim and Davies plotted against Robinson and Stokes (5) data. The results for a 1-2 electrolyte, K SO, are shown in Figure 4.5. The experimental data is smoothed data from Goldberg (13).

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