Comparative adsorption study of tert-pentanol and isopropanol on mercury and gallium from aqueous 0.5 M Na 2SO 4 at 32°C

Abstract

Adsorption of tert-pentanol and isopropanol on dropping mercury and gallium electrodes from aqueous 0.5 M Na 2SO 4 at 32°C was determined on the basis of capacitative charge measurements carried out by a computerized chronocoulometric apparatus. Adsorption measurements on Ga were carried out both in neutral solution and in acidic solutions of pH ≈ 3.5; in the latter medium, which avoids the formation of a submonolayer of Ga oxides induced by alcohol adsorption, the capacitative charge was corrected by a special procedure for the appreciable faradaic contribution due to hydrogen evolution. Surface concentrations and standard Gibbs energies of adsorption of both alcohols were determined on Hg as well as on Ga as a function of applied potential and charge density. Adsorptivities of both alcohols are lower on Ga than on Hg, especially at less negative charge densities. However, even at charge densities as negative as −12 μC cm −2, differences in the adsorptivity of the same alcohol on the two metals remain appreciable.