| Abstrakt: |
Current Pitzer activity coefficient models for the (H + Na + ClO4){aq} and (H + Na + Br){aq} systems are limited to ionic strengths <7 mol·kg–1. To accurately describe activity coefficients and solid solubilities in these systems, new Pitzer model parameters βNa,a(0), βNa,a(1), CNa,aϕ, θH,Nas, and ψH,Na,ClO4(a = ClO4–, Br–) and standard state chemical potentials (μi°/RT) were fit to the 298 K isopiestic and solid solubility data. The resulting NaClO4{aq} model reproduces the data, within their accuracy, to ionic strengths of approximately 18 mol·kg–1. No activity coefficient model parameters were necessary for the neutral species. Our dissociation constant of 130.36 for NaClO4·H2O is significantly different from the frequently cited value of 151.71. The θH,Nasderived from the (H + Na + ClO4){aq} system was tested for consistency against other acid systems containing soluble sodium salts, i.e., the (H + Na + Cl){aq}, (H + Na + Br){aq}, and (H + Na + NO3){aq} systems. A new Pitzer model for the NaBr{aq} system, which reproduces the data within their accuracy to solid saturation at 9.179 mol·kg–1, was produced for this test. The fitted θH,Nasparameter eliminated the need for the ψH,Na,aparameter (a = Cl–or Br–). |
