Water activities and stoichiometric osmotic coefficients for the systems MgB4O7+H2O and MgSO4+MgB4O7+H2O have been measured at 298.15 K by the isopiestic method using a improved isopiestic device; the saturated solution molalities of MgB4O7 are very low for these systems. These measurements extended from the near saturated molalities to supersaturation for the MgB4O7 binary solutions and from total molalities m (T) of 0.1787 to 2.2374 mol center dot kg(-1)with seven MgB4O7 molality fractions from 0.005 to 0.095 for the ternary solutions, respectively. The water activities of MgSO4 binary solutions (Y (B) = 0.0) were obtained by extrapolation of the present experimental results and were in agreement with the data from Rard and Miller (J. Chem. Eng. Data 26:33-38, 1981). The experimental stoichiometric osmotic coefficients are represented using Pitzer's ion-interaction model with a modified value of alpha (B2)=7.59 kg(1/2)center dot mol(-1/2) in the term,B-Mg,B4O7(phi) . Two sets of ion-interaction model parameters are presented for MgSO4+MgB4O7+H2O. The mixing parameters of the first set were evaluated using the presently calculated MgB4O7 single-salt parameters obtained from its binary-solution data. All the parameters relative to borate in the second set were estimated simultaneously from all the measured stoichiometric osmotic coefficient data for binary and ternary solutions in the present work, and were obtained with standard deviations of 0.0022 for MgB4O7 single salt-parameters and 0.0063 for the mixing parameters. The MgSO4 single-salt parameters reported by Rard and Miller (J. Chem. Eng. Data 26:33-38, 1981) were used for the evaluation of both sets of the ion-interaction parameters. The stoichiometric mean activity coefficients of the solutes for the systems are primarily calculated using Pitzer's standard equations for the activity coefficient with the same values of parameters and the exponential coefficients of alpha (1), alpha (2) and alpha (B2) for the osmotic coefficient model. The effects of the ionic interactions on the thermodynamic properties for the studied systems are discussed. Water activities and stoichiometric osmotic coefficients for the systems MgB4O7+H2O and MgSO4+MgB4O7+H2O have been measured at 298.15 K by the isopiestic method using a improved isopiestic device; the saturated solution molalities of MgB4O7 are very low for these systems. These measurements extended from the near saturated molalities to supersaturation for the MgB4O7 binary solutions and from total molalities m (T) of 0.1787 to 2.2374 mol center dot kg(-1)with seven MgB4O7 molality fractions from 0.005 to 0.095 for the ternary solutions, respectively. The water activities of MgSO4 binary solutions (Y (B) = 0.0) were obtained by extrapolation of the present experimental results and were in agreement with the data from Rard and Miller (J. Chem. Eng. Data 26:33-38, 1981). The experimental stoichiometric osmotic coefficients are represented using Pitzer's ion-interaction model with a modified value of alpha (B2)=7.59 kg(1/2)center dot mol(-1/2) in the term,B-Mg,B4O7(phi) . Two sets of ion-interaction model parameters are presented for MgSO4+MgB4O7+H2O. The mixing parameters of the first set were evaluated using the presently calculated MgB4O7 single-salt parameters obtained from its binary-solution data. All the parameters relative to borate in the second set were estimated simultaneously from all the measured stoichiometric osmotic coefficient data for binary and ternary solutions in the present work, and were obtained with standard deviations of 0.0022 for MgB4O7 single salt-parameters and 0.0063 for the mixing parameters. The MgSO4 single-salt parameters reported by Rard and Miller (J. Chem. Eng. Data 26:33-38, 1981) were used for the evaluation of both sets of the ion-interaction parameters. The stoichiometric mean activity coefficients of the solutes for the systems are primarily calculated using Pitzer's standard equations for the activity coefficient with the same values of parameters and the exponential coefficients of alpha (1), alpha (2) and alpha (B2) for the osmotic coefficient model. The effects of the ionic interactions on the thermodynamic properties for the studied systems are discussed.

Yin, Song Tao,Yao, Yan,Li, Bing,et al. Isopiestic studies of aqueous MgB4O7 and MgSO4+MgB4O7 at 298.15 k andrepresentation with Pitzer's ion-interaction model[J]. JOURNAL OF SOLUTION CHEMISTRY,2007,36(11-12):1745-1761.