ACTIVITY COEFFICIENTS OF AQUEOUS METHANOL SOLUTIONS

Abstract

the activity coefficients were in error by 0.008 for gamma /sub plus or minus / = 0.3261 in the dilute solution range or by 0.020 for gamma /sub plus or minus / = 9.760 in the most concentrated solutions of erbium chloride. All deviations in the activity coefficient gave an almost uniform mean deviation of 0.23%. These deviations in the activity coefficient correspond with those expected from the experimental procedure of this type of research. The errors concurred are: the error in analysis of each solution was of the order of 0.05% for molalities greater than one and from 0.10 to 0.15% for molalities less than one; and the reliability of the reference osmotic coefficient data is about 0.0010 in the osmotic coefficient. Since the molalities of two solutions must be known for the calculation of the rare-earth osmotic coefficient, a mean deviation of 0.0020 in its osmotic coefficient determined in this research is within the experimental precision of the isopiestic method. The osmotic and activity coefficients determined by Spedding and Saeger and by this research, for the rare-earth chlorides, show a marked increase across the series, particularly at high concentrations. For example, the activity coefficients at 3.4 molal are; La(3.303) < Nd(3.822) < Sm(4.087) < Gd(4.836) < Dy(5.539) < Er(6.372) < Y(6.504). The osmotic and activity coefficients of yttrium chloride behave like those of the heavy rareearth chlorides. The high activity coefficient of concentrated rare-earth chloride solutions strongly indicates that complete ionization of the electrolyte is far from being the case. The formation of complexes and polymerization of the electrolyte along with an increase in hydration, which decreases the water activity, all partly account for a high activity coefficient for the electrolyte. (auth)