Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

In this paper, the thermodynamic properties of a quaternary system including CaCl2 and Ca(NO3)2 as mixed electrolytes in the aqueous L-alanine mixture, were reported using the potentiometric method. The potentiometric measurements were performed on the galvanic cells of the type: (a) Ag-AgCl-CaCl2 (mC) , H2O-Ca-ISE, (b) NO3- ISE-Ca(NO3)2 (mB), L-alanine (mA = 0.2 mol kg-1), H2O-Ca-ISE, (c) Ag- AgCl-Ca(NO3)2 (mB), L-alanine (mA = 0.2 mol kg-1), H2O-Ca-ISE, and (d) Ag- AgCl-CaCl2 (m1), Ca(NO3)2 (m2), L-alanine (0.2 mol kg-1), H2O-Ca-ISE, over total ionic strengths from 0.0100 to 4.0000 mol kg-1 at T = (298.2, 303.2 and 308.2 ) K and P = 0.1 MPa. Different series of the salt molal ratios r(r=m_CaCl2/m_Ca(NO3)2= 0.1, 1.0, 2.5, 5.0, 7.5, and 10) and pure Ca(NO3)2 in mixed solvent system containing 0.2 mol kg-1 of L-alanine were used for the potentiometric measurements. The Ca2+ and NO3 - ion selective electrodes were prepared in our laboratory using related ionophores. Data analyze was performed based on Pitzer ion interaction model. At the beginning, the mixed ionic interaction parameters (theta_ClNO,psi_CaClNO ) were investigated according to Pitzer graphical method. After that, thermodynamic properties such as the mean activity coefficients, the osmotic coefficients, the solvent activity , the excess Gibbs free energy , the excess enthalpy and the excess entropy for electrolyte solutions were calculated. Moreover, the ratio of L-alanine activity coefficients in presence of electrolyte (gamma_A) to values of this property in absence of electrolyte (gamma_0 A ) was obtained by Scatchard equation.