Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The main goal of this work is to provide precise thermodynamic data about the ternary system (CaCl2 + Ca(NO3)2 + H2O), which may allow modeling its behavior. The Pitzer ion interaction model and Harned rule were used to illustrate the ternary electrolyte system. The activity coefficients were determined using a potentiometric method. The measurements were performed at T = 298.15 +- 0.1 K and at total ionic strengths from (0.0010 to 5.0000) mol kg 1. Different series of molal salt ratios were r 1/4 mCaCl2 mCaoNO3P2 = 1.00, 2.50, 5.00, 10.00 and 15.00. The PVC based calcium ion-selective electrode (Ca2+-ISE), and the Ag/AgCl electrode used in this work were prepared in our laboratory. The mixing Pitzer parameters (hClNO3 ;WCaClNO3 ) were determined for this system. Then these parameters were used to calculate thermodynamic properties such as the osmotic coefficients, the activity coefficients of Ca(NO3)2 in the mixture (c CaoNO3P2 ) and the excess Gibbs free energy (GE). The experimental results showed that both Pitzer model and Harned rule were suitable to be used satisfactorily to describe this system.