ELECTROSORPTION OF 1-BUTANOL AT THE MERCURY ELECTROLYTIC SOLUTION INTERFACE IN THE PRESENCE OF SPECIFICALLY ADSORBED ANIONS - A TEST OF THE BASIC FRUMKIN MODEL

The mercury-electrolytic solution interfacial tension gamma was measured at 25-degrees-C as a function of 1-butanol activity a(A) and polarization E measured against a saturated NaCl calomel electrode for 1-butanol reduced concentrations c/c0 from 0 to 0.5 at 50-mV intervals for 0.10 M electrolytes HClO4, KCl, KBr, and KI. For KCl, KBr, and KI the function ln(a(A)c0/c) Was found to vary linearly with c/c0 within experimental error; parameters for the linear functions are given. For HClO4, Values of ln(a(A)c0/c) were comparable to those for KCl for c/c0 > 0.2 but were irreproducible for lower values of c/c0. Plots of gamma(c/c0,E) with E referred to the electrocapillary maximum of the 0.10 M HClO4 and KCl base solutions (-0.477 V vs SSCE in both cases) for a given c/c0 for all four electrolytes were indistinguishable for E < -0.35 V, but as E became more positive than -0.35 V first the gamma(c/c0,E) curve for KI, then that for KBr, then that for KCl deviated negatively from that for HClO4. As c/c0 increased, the polarization required for divergence also increased. The basic Frumkin model for regular localized monolayer electrosorption was used to develop a master curve of pi/GAMMA(m)RT vs In Ba(A) With parameters GAMMA(m)RT, alpha, B0, C', and E(N) taken as the same for all electrolytes. These parameters and experimental values of gamma(0,E) permit determination of B(E)/B0, so that experimental points can be compared with the master curve. Results for E less-than-or-equal-to E' -0.1 with E' = 0.500, 0.300, and 0.000 V for KCl, KBr, and KI, fell quite close to the master curve for all values of a, with values of pi/GAMMA(m)RT deviating from it by more than 0.04 quite rare and no systematic pattern to deviations apparent. The basic Frumkin model, given its approximations and assumptions, is therefore remarkably satisfactory for data representation in this polarization range. At polarizations greater-than-or-equal-to E' -0.1, values of pi/GAMMA(m)RT lie increasingly higher than the master curve, indicating either additional contributions to pi/GAMMA(m)RT or underestimate of In B in the model. An empirical model based on specific anion adsorption within the complete organic monolayer was found capable of accounting for the deviations.