Dissociation constant of calcium sulphate from 25 to 50°C

Abstract

The e.m.f. of the cell Ag, AgCl | CaCl₂(m₁), CaSO₄(m₂)| Ca-exchange membrane | CaCl₂(0.1 mol kg^–1)| AgCl, Ag has been determined at 25, 40 and 50°C. Errors associated with drifting of the calcium ion-exchange electrode have been minimised by using a rapid method to determine E^⊖ and the Nernstian slope factor of the electrode pair before determining the e.m.f. of the above cell. The data were used to calculate values of the thermodynamic quantities K_d, ΔG^⊖, ΔH^⊖, ΔS^⊖ and ΔC^⊖_p for the dissociation of the CaSO₄ ion-pair.