THERMODYNAMIC PROPERTIES OF 0-6 MOL KG-1 AQUEOUS SULFURIC-ACID FROM 273.15 TO 328.15-K

Generalised equations are presented for an extended form of the Pitzer molality-based thermodynamic model, involving an ionic strength-depen dent third virial coefficient. Compatibility with the established form ulation is retained. Osmotic coefficients, emf measurements, degrees o f dissociation of the HSO4- ion, differential enthalpies of dilution a nd heat capacities for aqueous H2SO4 from 273.15 to 328.15 K, 0-6.1 mo l kg-1 and at 1 atm pressure have been critically evaluated. Treating this solution as the mixture H+-HSO4--SO42--H2O, and using hydrogen su lfate dissociation constants from the literature, the model parameters were fitted to the data yielding a self-consistent representation of activities, speciation and thermal properties together with the standa rd potentials of four electrochemical cells and standard-state heat ca pacities of the SO42- ion as functions of temperature. The model equat ions represent the experimental data accurately (without the use of mi xture parameters theta(HSO4,SO4) and psi(HSO4,SO4,H)), and should yiel d values of the osmotic coefficient that are suitable for use as an is opiestic standard over this temperature and molality range. The new mo del will also enable improved prediction of the properties of mixed ac idic sulfate systems.