Thermodynamics of proton dissociations from aqueous L-tartaric acid at temperatures 278.15 <= (T/K) <= 393.15 and at the pressure p = 0.35 MPa: apparent molar volumes and apparent molar heat capacities of L-tartaric acid and its sodium salts

摘要

Apparent molar volumes V_(#PHI) and apparent molar heat capacities C_(p,#PHI#) of aqueous solutions of L-tartaric acid, mono-sodium L-tartrate, and di-sodium L-tartrate have been measured at molalities 0.006 <= m/(mol (centre dot) kg~(-1)) <= 1.0, at temperatures 278.15 <= (T/K) <= 393.15, and at the pressure p = 0.35 MPa. Apparent molar volumes were obtained from density measurement using a vibrating-tube densimeter (DMA 512, Anton Paar, austria). Apparent molar heat capacities were obtained from heat capacity measurements using a twin fixed-cell, differential-output, power-compensation, temperature-scanning calorimeter (NanolDSC model 6100, Calorimetric Sciences Corporation, Spanish Fork, UT, U.S.A.). These results were also used to estimate the change in volume (m, T, #DELTA#_rV_m) and the change in heat capacity (m, T, #DELTA#_rC_(p,m)) for the two stepwise proton dissociation reactions of aqueous L-tartaric acid. The (m, T, #DELTA#_rC_(p,m)) surfaces for each proton dissociation reaction were integrated numerically to obtain estimates of the change in enthalpy (m, T, #DELTA#_rH_m) and proton dissociation molality quotients (m, T, pQ_a). These integrated results greatly extend the ranges of m and T over which precise thermodynamic information is available for the two dissociation reactions of aqueous L-tartaric acid.