Osmotic and activity coefficients of sodium sulphate in water from 50 to 150 °C

The vapour pressure lowering, ΔP, of sodium sulphate solutions in water was measured in the concentration range 0.4 to 1.8 m and the temperature range 50 to 150 °C by the use of a differential manometer. ΔP values were used to calculate the osmotic coefficient of sodium sulphate solutions. Pitzer's equation for osmotic coefficients was used to evaluate βMX(0), βMX(1), and at each temperature. An attempt has been made to explain the changes in these constants in terms of the ion–ion and ion–solvent interactions. Using these constants, the mean activity coefficients, γ±, of sodium sulphate were calculated at different temperatures and concentrations using Pitzer's equation.