The real standard potential on the aqueous hydrogen scale of the silver/silver chloride electrode in methanol: the surface potential of methanol

Abstract

The compensating potential difference (cpd) has been measured for the voltaic cell constructed from a mercury jet reference electrode and a silver/silver chloride electrode in a methanolic solution of KCl, in the KC1 molality range 3×10 −5 < m 1 < 0.03. The results show that the surface potential of a KCl solution in methanol becomes steadily less negative with increasing KCl concentration. A quantitative electrostatic model for the interaction of ions in solution with the permanent dipole layer at the surface of a liquid is critically examined and we conclude that pure methanol has a surface potential of at least −90 mV although our data are consistent with a previously-recommended value of −230 mV. The standard real potential of the half-cell Cl − (methanol)|AgCl,Ag on the aqueous hydrogen scale is defined and found by extrapolation to be −0.321 ±0.001 V; this fixes the E XXX values on the real electrode potential scale in methanol at 298 K.