Activity Coefficient Measurements and Thermodynamic Modeling of (CaCl2 + l-Alanine + Water) System Based on Potentiometric Determination at T = (298.2, 303.2, and 308.2) K

Abstract

In this work, the thermodynamic properties of the ternary (CaCl2 + l-alanine + water) system, using the potentiometric method, were reported. The potentiometric measurements were performed on the galvanic cell of the type: Ag–AgCl|CaCl2·2H2O (m), l-alanine (mA), H2O|Ca–ISE, in various mixed solvent systems containing 0.0 mol·kg–1, 0.1 mol·kg–1, 0.2 mol·kg–1, 0.3 mol·kg–1, and 0.4 mol·kg–1 of l-alanine, over total ionic strengths from 0.0100 mol·kg–1 to 3.0000 mol·kg–1 at T = (298.2, 303.2, and 308.2) K and P = 0.1 MPa. The Ca–ISE was prepared in our laboratory using the ionophore treated by carbon nanotubes. The Debye–Huckel extended equation, Pitzer ion interaction and PSC models were used to correlate the experimental data. The unknown parameters were evaluated and utilized to calculate the thermodynamic properties such as the mean activity coefficients, the osmotic coefficients, the solvent activity, and the excess Gibbs free energy for underinvestigated electrolyte solutions.