Abstract
The concentration curve of mean activity coefficient to the required power was fitted by a product function. The product function can be factorized in factor functions which represent the concentration dependence of the single-ion species (J Solid State Electrochem, in press, 1). With a simplified procedure of this method, it is possible to split the mean activity coefficients into the individual parts for the ionic species within the extended Debye–Hückel concentration range. This method is applicable to all strong electrolytes because it is not necessary to have further data or additional assumptions.
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Notes
Concerning the case k = lower bound of summation 1 and upper bound of summation 3, the relationship (4) is written in the paper by Ferse and Müller [1] dissolved in summands with a different designation of the parameters:
$$ \gamma_{\pm }^{{{\nu_{ + }} + {\nu_{ - }}}}(J) = \bar{\gamma }_{\text{C}}^{{{\nu_{ + }}}}(J) \cdot \bar{\gamma }_{\text{A}}^{{{\nu_{ - }}}}(J) \approx {\left[ {{c_1}{e^{{{{c'}_7} \cdot {J^{{\frac{1}{2}}}}}}} + {c_3}{e^{{{c_9} \cdot J}}} + {c_5}{e^{{{c_{{11}}} \cdot {J^{{\frac{3}{2}}}}}}}} \right]^{{{\nu_{ + }}}}}{\left[ {{c_2}{e^{{{{c'}_8} \cdot {J^{{\frac{1}{2}}}}}}} + {c_4}{e^{{{c_{{10}}} \cdot J}}} + {c_6}{e^{{{c_{{12}}} \cdot {J^{{\frac{3}{2}}}}}}}} \right]^{{{\nu_{ - }}}}} $$The following values [20] are used after the year 1977: A′ = 1.17625 (A = 0.510839), B = 0.32866; all values are valid for aqueous solutions and a temperature of 298.15 K.
Hamer and Wu [21], for example, used the following relationship (11) for the calculation of the mean activity coefficients but for an extended concentration range:
$$ \log {\gamma_{\pm }} = \frac{{ - {\text{A}}\left| {{z_{\text{C}}} \cdot {z_{\text{A}}}} \right|\sqrt {J} }}{{1 + B*\sqrt {J} }} + \beta \cdot J + C \cdot {J^2} + D \cdot {J^3} + ... $$(11)B*, ß, C, D…: empirical constants, the values are different for all electrolytes.
Note: B* in (11) is not identical with “B \( \tilde{a} \)” in the extended Debye–Hückel Eq. 10!
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Acknowledgment
I want to express my sincere thanks to Prof. Dr. Waldfried Plieth, Technische Universität Dresden, Germany. This paper could not have been realized without his encouraging interest and his decisive support.
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Ferse, A. Estimation of activity coefficients of ionic species of aqueous strong electrolytes within the extended Debye–Hückel concentration range. J Solid State Electrochem 15, 2177–2184 (2011). https://doi.org/10.1007/s10008-011-1530-5
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DOI: https://doi.org/10.1007/s10008-011-1530-5