Isopiestic determination of the osmotic and activity coefficients of {(1 − y)H 2SO 4 + yNa 2SO 4}(aq) at the temperature 298.15 K II. Results for y = (0.12471, 0.24962, and 0.37439)

Abstract

Isopiestic vapor-pressure measurements were made for {(1 − y)H2SO4 + yNa2SO4}(aq) with y = (0.12471, 0.24962, and 0.37439), at molalities from 0.19262 mol·kg−1 to 0.19501 mol·kg−1 up to the crystallization molalities (12.813 mol·kg−1 to 14.960 mol·kg−1) at the temperature 298.15 K. We previously reported results for y = 0.5 to y = 0.84920. These highest molalities studied represent the highest degree of supersaturation that could be achieved by isothermal removal of solvent. Comparison of the variation of these highest molalities with published solubilities suggests that solid Na2SO4 · 10H2O precipitated for y = 0.70189 and y = 0.84920, that Na3H(SO4)2 {or Na3H(SO4)2 · H2O}) precipitated for y = 0.24962 to y = 0.55595, and that NaHSO4 · H2O precipitated for y = 0.12471. If osmotic coefficients for the solutions are calculated by using stoichiometric molalities of Na2SO4 and H2SO4 and assuming they are strong 1–2 electrolytes, then derived osmotic coefficients fall significantly below values predicted from the Scatchard neutral-electrolyte binary-solution mixing approximation. For y > 0.7 and I > 3 mol · kg−1, the osmotic coefficients generally fall significantly below those of both limiting binary solutions; but for y 0.5 mol · kg−1.