Activity coefficients of CaCl sub(2) in (serine or proline + water) mixtures at T = 298.15 K

Activity coefficients for the (CaCl sub(2) + amino acid + water) system were determined at a temperature of 298.15 K using ion-selective electrodes. The range of molalities of CaCl sub(2) is (0.01 to 0.20) mol super(. kg) super(-)1 and that of amino acids is (0.10 to 0.40) mol super(. kg) super(-)1 The activity coefficients obtained from the Debye-Hueckel extended equation and the Pitzer equation are in good agreement with each other. Results show that the interactions between CaCl sub(2) and amino acid are controlled mainly by the electrostatic interactions (attraction). Gibbs free energy interaction parameters (g sub(EA)) and salting constants (k sub(S)) are positive, indicating that these amino acids are salted out by CaCl sub(2). These results are discussed based on group additivity model.