电势法研究NaBr在甲醇-水混合溶剂中298.15K下的热力学性质

用Na离子选择性电极NaBr(m),MeOH(w),H_2O(100-w)Br离子选择性电极组成的电池测定NaBr在甲醇含量为0%、10%、20%、40%、60%、80%、90%和100%的甲醇-水混合溶剂,浓度在0.01～3.0mol/kg之间的平衡电势.用Pitzer方程关联实验结果得到每个实验点的NaBr的平均活度系数.结果发现,在一定的溶剂比例下,NaBr的平均活度系数先随它的浓度增加而下降,然后上升;当NaBr浓度固定时,它的平均活度系数随溶剂中甲醇含量增加而下降.NaBr在甲醇中有微弱的缔合.

THERMODYNAMIC PROPERTIES FOR SODIUM BROMIDE-METHANOL-WATER SYSTEM AT 298.15K BY E.M.F. MEASUREMENTS

Electromotive force measurements of the cell Na ion-selective elec-trode(glass) |NaBr(m), MeOH(w), H2O(100-w)|Br ion-selective electrode (solid state)were made at molalities of NaBr ranging from 0.01 to 3.0 in the mixed solvent of methanol-water containing 0, 10, 20, 40, 60, 80, 90, and 100 weight% methanol, respectively, at 298. 15K. Calculations of standard cell potential were made by using the Pitzer equation, and then the mean activity coefficient values of NaBr were evaluated. The association constant of NaBr in methanol were evaluated from the experimental E. M. F. data by using the Pitzer-Simonson equation extended to the binary systems containing ion pairing. The weak association of NaBr in methanol was shown. At each fixed solvent composition, the mean activity coefficients of NaBr first decreased and then increased with rising NaBr molality. At each fixed NaBr molality, they decreased with an increase of methanol in solvent mixtures.