Estimation of transfer activity coefficients for single ions between dipolar aprotic solvents from the E.M.F. of cells with liquid junction

Abstract

Transfer activity coefficients for the sodium ion, log_mγ_Na, between pairs of dipolar aprotic solvents were estimated from the e.m.f. of cells consisting of two sodium-selective electrodes in different solvents connected by a salt-bridge of triisoamylbutylammonium tetraphenylborate [(tab⁺)BPh₄^-], or tetraethylammonium picrate (Et₄NPic), or tetraethylammonium perchlorate (Et₄NclO4). The solvents were: acetonitrile (MeCN), N,N-dimethylformamide (HCONMe₂), dimethyl sulfoxide (Me₂SO), propylene carbonate (pcar), and N-methylformamide (HCONHMe). Values of log_mγ_NA were estimated first by neglecting the liquid-junction potential E, and then, for some systems, by applying an E_j correction from theory. A novel method of estimating transfer activity coefficients for single ions, based on the E_j equation, was demonstrated on the (tab⁺) and Pic^-ions. Transfer activity coefficients for the hydrogen ion between MeCN and HCONMe₂ as well as MeCN and Me₂SO were similarly estimated from the e.m.f. of two pH (glass) electrodes immersed in buffer media in the above pairs of solvents.