MEASUREMENTS AND CORRELATION OF OSMOTIC COEFFICIENTS AND EVALUATION OF VAPOR PRESSURE FOR SOLUTIONS OF KCH₃COO AND NaCH₃COO IN METHANOL AT 25 °C^†

Karamat Nasirzadeh,^a,b* Roland Neueder^b

^a Department of Chemistry, Faculty of Science, Azerbaijan University of Tarbiat Moallem,Tabriz, Iran

^b Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany

Fax: +49-941-9434532; E-mail: Karamat.nasirzadeh@chemie.uni-regensburg.de

^†This paper is dedicated to Prof. Josef Barthel in honour of his 75^th birthday.

Abstract

The osmotic coefficients of potassium acetate and sodium acetate 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 0.17-2.51 mol×kg^-1 for potassium acetate and 0.25-1.76 mol×kg^-1 for sodium acetate. The system of equations of Pitzer–Mayorga and MSA-NRTL were used to fit osmotic coefficients. The parameters from the fit were used to calculate the vapor pressures. The osmotic coefficient data are successfully correlated with these models, which provide reliable predictions of vapor pressures.

Key words: osmotic coefficient, isopiestic, methanol, models