Studies on the equilibria of o-phthalic and phosphoric acids in mixed dimethyl sulphoxide—water mixture

Abstract

The secondary dissociation constants of o-phthalic and phosphoric acids have been determined in 50% w/w dimethyl sulphoxide—water from reversible emf measurements of the cell of the type: Pt, H 2 (1 atm), M 2A (m), MHA (m), MCl, AgCl; Ag at different temperatures (288.15–308.15 K) and at different ionic strengths. To minimize the unsteadiness in potential measurements palladium-coated platinum electrodes have been used. The large set of such emf values has been analysed in terms of a multi-linear regression method recommended in recent IUPAC documents. The thermodynamic values Δ G°, Δ H°, Δ S°, for the respective equilibria were estimated. The possibility of using these acids as a basis for some buffer solutions in 50% dimethyl sulphoxide (Me 2SO)-water mixture is discussed.