Thermodynamics of hydrochloric acid in propylene carbonate–water mixtures from e.m.f. measurements between 5 and 45 °C

Abstract

E.m.f. measurements of cells of the type Pt,H₂(g, 1 atm)∣HCl(m), PC(X), H₂O(100 –X)∣AgCl, Ag at five temperatures from 5 to 45 °C have been used to derive (i) the standard potentials of the Ag–AgCl electrode, (ii) the mean molal activity coefficient of HCl, (iii) the primary medium effects, and (iv) the thermodynamic constants for the transfer of HCl from water to the respective propylene carbonate–water mixtures. The molality of the acid ranged from 0·005 to 0·2 mol kg^–1. The standard e.m.f. varied with temperature (t/°C) according to equations (a)–(c) where X=%(W/W) of propylene carbonate. The results of the thermodynamic functions have been interpreted in terms of the acid–base properties and the breakdown of the solvent structure. (a)E_m°(X= 5)= 0·2209 – 5·635 × 10^–4(t– 25)– 3·293 × 10^–6(t– 25)²(b)E_m°(X= 10)= 0·2188 – 5·843 × 10^–4(t– 25)– 5·165 × 10^–6(t– 25)²(c)E_m°(X= 20)= 0·2130 – 6·616 × 10^–4(t– 25)– 2·725 × 10^–7(t– 25)²