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 chlorid

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 Vϕ and the heat capacities to calculate apparent molar heat capacities Cp,ϕ for these solutions. We used our results and values of Vϕ(T, m) and Cp,ϕ(T, m) for HCl(aq), NaOH(aq), NaCl(aq) from the literature to calculate parameters for ΔrCp,m(T, m) for the first and second proton dissociations from protonated aqueous cationic glycine. We then integrated this value of ΔrCp,m(T, m) in an iterative algorithm, using Young’s Rule to account for the effects of speciation and chemical relaxation on the observed Vϕ and Cp,ϕ of the solutions. This procedure yielded parameters for Vϕ(T, m) and Cp,ϕ(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 ΔrCp,m, ΔrHm, ΔrVm, and pQa for the first and second proton dissociations from protonated aqueous glycine as functions of T and m.