Standard potentials of silver-silver bromide electrode in propylene glycol-water-mixtures at different temperatures and the related thermodynamic quantities

Abstract

Standard electrode potentials of the sl lver4lver bromide electrode were determined at five temperatures In the temperature range 5-45 O C in 20,40,60, and 80 wt % diethylene glycol-water mixtures by EMF measurements on the cell Pt, HB(g, 1 atm)IHBr(m), diethylene glycol(X)water( 01 AgBr-Ag. The primary medium effects, the mean molal activity coefficients of HBr In the concentration range 0.01-0.08 mol kg-', and the various thermodynamic parameters for the transfer of HBr from water to these media at 25 O C are also reported. The standard molal potential, in the various solvent mixtures has been expressed as a function of temperature. The variation of the thermodynamic parameters for the transfer process with solvent composition has been discussed both In terms of the basicity of the solvent mixtures and also their structural effects on the transfer process. The standard molar free energy of transfer, linear function of In & (9, = volume fraction of water) in the various solvent mixtures up to about 60 wt % diethylene glycol and, from the slope, the number of water molecules coordinated to HBr, n, was calculated to be 0.85. was found to be a