Measurement and prediction of water activity in electrolyte solutions by a modified ASOG group contribution method

A set of new ionic type functional groups for the prediction of water activities (aw) in aqueous solutions of electrolyte solutes using the ASOG group contribution method is proposed. Previously published experimental data on water activities, osmotic coefficients and freezing temperatures for binary solutions of electrolyte salts and water at different temperatures were used to calculate interaction parameters. With such parameters, values of aw for binary (14), ternary (28) and quaternary (3) systems, at different temperatures, were predicted and compared with experimental data. This data included both published and new data, measured with an electric hygrometer, for sodium nitrate (at 20°C) and potassium nitrate (at 20°C and 30°C). Calculated average relative deviations of aw predictions using the ASOG method were 0.21%, 0.28% and 0.20% respectively.