| Abstrakt: |
The problem of single-ion activity coefficients is addressed, primarily, in view of application of ion-selective electrodes (ISEs). A brief historical survey is followed by the consideration of the information delivered by measurements of the EMF of galvanic cells with and without liquid junction. It is shown that obtaining practically relevant data, the content of a particular ion in mixed solution requires measurements with cells with liquid junction. These measurements, in turn, require the use of individual ion activities. Several conventions aimed at accessing these values are discussed. The above-mentioned issues can be useful for teaching electrochemistry. An empirical modification of the Davies' equation is proposed: l o g γ i = - A z i 2 I 1 + a Kiell B I + D i z i I . The values of individual, ion-specific parameters a Kiell and D i have been found based on the best agreement with literature data on the mean electrolyte activity coefficients. Activity coefficients of cation, γ + , and anion, γ - , are calculated separately using the equation proposed, and the respective mean electrolyte activity coefficient is calculated according to its definition using the obtained single-ion activity coefficients: γ ± υ = γ + υ + γ - υ - . The calculated mean electrolyte activity coefficients are compared with literature data on mean electrolyte activities of 53 electrolytes (at 25 °C). The consistency of the proposed values of the individual ion parameters is achieved: for a particular ion, they remain the same in any electrolyte. For KCl and CaCl2, it is also checked whether individual ion parameter values are suitable over the temperature range from 15 to 35 °C (relevant in view of ISE application), and whether these values allow for a consistent interpretation of the ISE response in pure and mixed solutions. [ABSTRACT FROM AUTHOR] |
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