Calculation of liquid junction potentials

Abstract Equations and methods for the calculation of liquid junction potentials are reported. They are applicable to homoionic junctions over large molality ranges. In the general equation for E j , we have used t i vs. m dependence of the DHB equation [R. Dorta-Rodriguez, F. Hernandez-Luis, M. Barrera-Niebla, J. Electroanal. Chem., in press], while for mean ionic activity coefficient, we use the equations of Scatchard (S) or Pitzer (P), being single-ion activity coefficients evaluated according to Debye-Huckel convention. We have written two QBasic programmes (DHB-S and DHB-P) which generate E j values according to a code (electrolyte name) that is input in addition to the boundary solution molalities. The storages needed for both programmes are the stoichiometry and the parameters of the DHB and S or P equations. They are stored for some thirty electrolytes and allow us to calculate potentials across homoionic junctions with the ionic strength ranging from infinite dilution to solubility. Some procedures for determining E j from potentials of electrochemical cells are sketched. The agreement between these values and those calculated with the aforementioned programmes is very good. Likewise, for some electrolytes, extensive data files were generated with the above cited programmes to obtain, by tridimensional fit, functional equations E j ( m 1 , m 2 ) for calculating E j values easily. Finally, some instances of application in ISE-potentiometry, thermodynamics and kinetics of electrodes and mercury|electrolyte interface studies of methods reported here are given. In the later application, we have derived an approximate t i ( c ) equation for 1:2 electrolytes in water at 25°C.

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