Thermodynamics of hydrochloric acid in 95 volume per cent (92.41 mass per cent) ethanol from e.m.f. measurements at 5 to 50°C

Abstract

Electromotive-force measurements of cells of the type Pt/H 2/HCl( m) in EtOH + H 2O/ AgCl/Ag at 10 temperatures from 5 to 50 °C have been used to derive (a) the standard e.m.f. of the cell of 92.41 mass per cent ethanol, (b) the activity coefficient of hydrochloric acid, (c) the relative partial molal enthalpy and heat capacity of HCl, and (d) the thermodynamic constants for the transfer of HCl from water to 92.41 mass per cent ethanol. The molality of the acid ranged from 0.0099 to 1.085 mol kg −1. To obtain the standard e.m.f. it was necessary to correct for ion-pair formation and to use the extended terms of the Debye-Hückel theory. The ion-size parameter, chosen to minimize the sum of the squares of the deviations, varied only slightly with temperature, from 3.97 Å at 5 °C to 4.31 Å at 50 °C.