Dissociation Constants of Oxalic Acid in Aqueous Sodium Chloride and Sodium Trifluoromethanesulfonate Media to 175 °C

Authors

Richard Kettler, University of Nebraska-LincolnFollow
David J. Wesolowski, Oak Ridge National Laboratory
Donald A. Palmer, Oak Ridge National Laboratory

Date of this Version

1998

Comments

Published in J. Chem. Eng. Data 1998, 43, 337-350

Abstract

The first and second molal dissociation constants of oxalic acid were measured potentiometrically in a concentration cell fitted with hydrogen electrodes. Measurements were made at six temperatures ranging from 5 °C to 125 °C at four ionic strengths ranging from 0.1 mol•kg^-1 to 1.0 mol•kg^-1 (NaCl and NaCF₃-SO₃). The second molal dissociation constant was measured in NaCF₃SO₃ media only. The data obtained in this study were combined with the corresponding literature values, including a number of recalculated Harned cell and concentration cell measurements and previous results from this laboratory. Data for first molal dissociation constant obtained in the two ionic media were regressed simultaneously to yield a five-term equation that describes the dissociation in the anionic form. The thermodynamic properties obtained at 25 °C and infinite dilution are: log K_1a = -1.401 ± 0.052, ΔH_1a = (-0.7 ± 0.7) kJ•mol^-1, ΔS_1a = (-29 ± 2) J•K^-1•mol^-1, and ΔC_p,1a = (-231 ± 6) J•K^-1•mol^-1. Similar treatment of the original and recalculated data for the second molal dissociation constant yielded a nine-term equation and the following values at 25 °C and infinite dilution: log K_2a = -4.264 ± 0.014, ΔH_2a = (-7.3 ± 0.5) kJ•mol^-1, ΔS_2a = (-106 ± 2) J•K^-1•mol^-1, and ΔC_p,2a = (-229 ± 27) J•K^-1•mol^-1.