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 [Formula: see text] 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.