Standard potentials of silver–silver chloride electrode at different temperatures and transfer energetics of hydrochloric acid in urea + water mixtures

Abstract

Standard potentials (E°) of the Ag–AgCl electrode in four different compositions of urea + water mixtures at seven different temperatures from 10 to 40°C have been determined from the e.m.f. measurements of cells of the type: Pt, H₂(g, 1 atm)|HCl(m), urea + water mixtures|AgCl–Ag. These values have been utilized to evaluate the transfer energetics (ΔG^°_t, TΔS^°_t and ΔH^°_t) accompanying the transfer of 1 mol of HCl from the standard state in water to the standard state in urea + water mixtures. Attempts have been made to explain the transfer energetics in the light of ion-solvent interactions and the structural contributions of the solvents. A detailed analysis of entropy changes accompanying the transfer process indicates that at about 5–7 m of urea there is an enhancement of the structure of the urea + water mixtures possibly due to the formation of hydrogen-bonded urea-water complex.