EVALUATION OF IONIC AND SOLVENT COMPONENTS OF THE LIQUID-JUNCTION POTENTIAL BETWEEN AQUEOUS AND SEVERAL AQUO-ORGANIC SOLUTIONS

Values of E(j,ion), the ionic component of the liquid-junction potenti al E(j), were calculated for the HCl,H2O \ HCl,S2 and KCl,H2O \ KCl,S2 junctions, where S2 was EtOH-H2O, HCONMe2-H2O and Me2SO-H2O solvents, and for the AgNO3,H2O \ AgNO3,MeCN-H2O junction, over the entire mixe d-solvent ranges. Both the old approximate equation for E(j,ion) and o ur improved equation, which accounts for the variation of the ionic tr ansport numbers t and chemical potentials G(o) in the interphase regio n, were used. Significant differences between the two equations were o bserved for systems where the t and DELTA(t)G(o) functions displayed e xtrema against the mixed-solvent composition. The highest E(j,ion) val ue was 395 mV, for the HCl,H2O \ HCl,Me2SO junction. Values of E(j,s), the solvent component of E(j), were calculated by subtracting the cor responding E(j,ion) values from the total E(j), which was evaluated in each case from the e.m.f. of a cell with the liquid junction of inter est and the transfer activity coefficient of the electroactive ion, es timated by the tetraphenylborate assumption. The magnitude of E(j,s) w as significant for the junctions between H2O and most of the solvents, and was particularly large for those involving dipolar aprotic solven ts and highly solvated ions. The maximum E(j,s) value was -201 mV, obs erved for the junction HCl,H2O \ HCl,100% Me2SO.