Thermodynamics of proton dissociations from aqueous glycine at temperatures from 278.15 to 393.15 K,molalities from 0 to 1.0 mol · kg?1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of glycine,glycinium chloride,and sodium glycinate

We have measured the densities of aqueous solutions of glycine, glycine plus equimolal HCl, and glycine plus equimolal NaOH at temperatures 278.15 ? T/K ? 368.15, molalities 0.01 ? m/mol · kg^?1 ? 1.0, and at 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 fixed-cell differential scanning calorimeter. We used the densities to calculate apparent molar volumes V_? and the heat capacities to calculate apparent molar heat capacities C_p,? for these solutions. We used our results and values of V_?(T, m) and C_p,?(T, m) for HCl(aq), NaOH(aq), NaCl(aq) from the literature to calculate parameters for Δ_rC_p,m(T, m) for the first and second proton dissociations from protonated aqueous cationic glycine. We then integrated this value of Δ_rC_p,m(T, m) in an iterative algorithm, using Young’s Rule to account for the effects of speciation and chemical relaxation on the observed V_? and C_p,? of the solutions. This procedure yielded parameters for V_?(T, m) and C_p,?(T, m) for glycinium chloride {H₂Gly⁺Cl^?(aq)} and sodium glycinate {Na⁺Gly^?(aq)} which successfully modeled our observed results. We have then calculated values of Δ_rC_p,m, Δ_rH_m, Δ_rV_m, and pQ_a for the first and second proton dissociations from protonated aqueous glycine as functions of T and m.