Isopiestic determination of osmotic coefficients and evaluation of vapor pressures for solutions of sodium bromide and sodium thiocyanate in methanal at 25 °C

Abstract

The osmotic coefficients of sodium bromide and sodium thiocyanate in methanol have been measured by the isopiestic method at 25 °C. Sodium iodide was used as isopiestic standard for the calculation of osmotic coefficients. The molality ranges covered in this study correspond to about 0.17–1.56 mol·Kg −1 for NaBr and 0.15–3.43 mol·kg −1 for NaSCN. Experimental osmotic coefficient data are reliably represented by the Pitzer model (with and without the β (2) term), self-consistent local composition model (SCLC) and modified self-consistent local composition model (MSCLC). The parameters from the fit were used to calculate the vapor pressures. The osmotic coefficient data are successfully correlated with these models, and the models provide reliable predication of vapor pressures.