Comparison of acidities in molten hydrogenosulphates and their eutectics

Acidity in pure hydrogenosulphates NaHSO₄, KHSO₄, NH₄HSO₄ and in their eutectics (Na-K)HSO₄, (K-NH₄)HSO₄ and (NH₄-Na)HSO₄, was studied, at t=200°C and P(H₂O) =0.03 atm, by using an indicator glass-electrode. The values of the constants of autoprotolysis and of the solubilities of alkaline and ammonium sulphates have been determined for each of the molten salts considered. The acidity ranges available in these solvents were then compared by means of a single acidity scale referring to pure sulphuric acid. This comparison was made possible by mearusing, with a transference method, the vapour pressures of the sulphuric acid above its solutions in hydrogenosulphates and their eutectics. So, it demonstrated that the more acidic media are obtained in the eutectic (Na-K)HSO₄, and the more basic ones in NH₄HSO₄. Moreover, various thermodynamic functions, and especially, the standard entropies of the pure hydrogenosulphates, have been determined