Thermodynamics of the cell Pt | H2(p)| HCl (m)| AgCl| Ag and primary medium effects upon HCl in (glycerol + water) solvents

Abstract

The electromotive force (e.m.f.)E of the cellPt|H2(p)|HCl(m) in Z|AgCl|Ag in {glycerol (G) + water (W)} solvents, Z = (G + W), up to glycerol mass fraction wG= 0.7 has been measured within the temperature range from 273.15 K to 313.15 K at HCl molalities up to 0.1mol · kg−1. On this basis, the standard molar e.m.f. Em∘values pertaining to such solvent mixtures have been obtained, and have been combined with sparse literature data for optimization. At glycerol mass fractions up towG≈ 0.5, at constant temperature,Em∘ shows a linear dependence on the glycerol mole fractionxG and, in parallel, Ec∘(on the amount-of-substance concentration scale) shows linear dependence on the glycerol volume fractionϕG . The primary medium effect upon HCl, defined as the difference (Ec∘)W− (Ec∘)Z, has been considered as a function of the water volume fraction ϕWin terms of Feakins and French’s theory: this would lead to a primary hydration number n(hydr) = 2.4 for HCl, in good agreement with previous results obtained with solvents other than (glycerol + water). In this connection, some basic methodological aspects are discussed. Ancillary values of the densities ρZof the relevant solvent mixtures, which were hitherto unavailable and are necessary for the data processing leading toEm∘ , have also been measured.