A SINGLE SCALE FOR ION ACTIVITIES AND ELECTRODE POTENTIALS IN ETHANOL-WATER SOLVENTS BASED ON TRIISOAMYLBUTYLAMMONIUM TETRAPHENYLBORATE ASSUMPTION

Medium effects for individual ions enable us to express standard electrode potentials and ion activities in different solvents on a single aqueous scale and to evaluate liquid-junction potentials at aqueous-nonaqueous interphases. Existing methods for the estimation of medium effects of single ions are summarized. In the present approach, the medium effect logmγ of triisoamyl-n-butylammonium tetraphenylborate (TAB BPh4) is apportioned equally between the anion and the cation. On this basis, values of log mγ are estimated for H+, K+, Cl-, TAB+, BPh4-, and picrate ions throughout ethanol-water range. In ethanol-water mixtures, the solvation energy of the proton is lower than in the pure solvents and passes through a minimum. Conventional Eo's in ethanol when referred to the aqueous SHE become positive by about 0.1 V. The residual liquid-junction potential between an ethanoiic buffer and an aqueous KCl bridge is of the order of 60 mV. © 1969, American Chemical Society. All rights reserved.