We have measured the densities of aqueous solutions of alanine, alanine plus equimolal HCl, and alanine plus equimolal NaOH at temperatures 278.15 <= T/K <= 368.15, at molalities 0.0075 <= m/mol center dot kg(-1) <= 1.0, and at the pressure p = 0.35 MPa using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 <= T/K <= 393.15 and at the same m and p using a twin fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V-phi, and the heat capacities to calculate apparent molar heat capacities C-p,C-phi for these solutions. We used our results and values from the literature for V-phi(T, m) and C-p,C-phi(T, m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Delta C-r(p,m)(T, m) for ionization of water to calculate parameters for A, Cp,.(T, m) for the two proton dissociations from protonated aqueous cationic alanine. We integrated these results in an iterative algorithm using Young's Rule to account for the effects of speciation and chemical relaxation on V-phi(Tm) and C-p,C-phi(T, rn). This procedure yielded parameters for V-phi(T, m) and C-p,C-phi(T, m) for alaninium chloride {H(2)Ala(+)Cl(-)(aq)} and for sodium alaninate {Na(+)Ala(-)(aq)} which successfully modeled our observed results. Values are given for Delta C-r(p,m), Delta H-r(m), pQ(a), Delta S-r(m), and Delta V-r(m) for the first and second proton dissociations from protonated aqueous alanine as functions of T and M. (c) 2005 Elsevier Ltd. All rights reserved.