Osmotic and activity coefficients of some simple borates in aqueous solution at 25°

Abstract

Activity coefficients for sodium tetraborate, potassium tetraborate, sodium metaborate, sodium fluoroborate, and orthoboric acid were derived from isopiestic vapor pressure measurements. The osmotic behavior of sodium tetraborate, at concentrations up to its solubility limit, was the same as that of the more soluble potassium salt. The mean activity coefficients of both tetraborates were quite low: 0.355 at 0.1 m; the activity coefficients of sodium metaborate and fluoroborate were less than those of sodium chloride, indicating partial association in solution.The boric acid results were not very reliable because boric acid apparently volatilized during the measurements, but the results obtained indicated that it behaves like a non-electrolyte at all concentrations up to saturation, with an activity coefficient never less than 0.92.