Abstract:Mean activity coefficients of NaBr in NaBr-Na2B4O7-H2O system had been determined in the ionic strength ranging from 0.01 to 0.50 mol/kg at 298.15K by the EMF method. The mean activity coefficients were compared with those ionic strength scores of Na2B4O7 in the mixture solution. The results show that the determination of the mean activity coefficients of NaBr is reliable and the mean activity coefficients of NaBr increase with increasing of the ionic strength scores of Na2B4O7 in the mixture solution in the ionic strength range from 0.01 to 0.50 mol/kg.Pitzer ion interaction parameters that were not reported were evaluated from present measurements of the mean activity coefficients of NaBr.