Earth and Atmospheric Sciences, Department of


Date of this Version



Published in Journal of Solution Chemistry, Vol. 20, No. 9,1991


The first and second molal dissociation quotienls of oxalic acid were measured potenliometrically in a concentration cell filled with hydrogen electrodes. The emf of oxalic acid-bioxalate solutions was measured relative to an HCI standard solution from 25 to 125°C over 25° intervals at nine ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The molal dissociation quotients and available literature data were treated in the all anionic form by a five-term equation that yielded the following thermodynamic quantities at infinite dilution and 25°C: logKIa = -1.277±0.010, ΔHl̊a = -4.1± 1.1 kJ-mol-1, ΔSl̊a = 38±4 J-K-1 mol-1, and ΔCp̊,la = -168±41 J-K-1-mol-1. Similar measurements of the bioxalateoxalate system were made at 25° intervals from 0 to 175°C at seven ionic strengths from 0.1 to 5.0m. A similar regression of the experimentallyderived and published equilibrium quotients using a seven-term equation yielded the following values at infinite dilution and 25°C: log K2a = -4.275±0.006, ΔH2̊a = -6.8±0.5 kJ-mol-1, ΔS2̊a = -105±2 J-K-1mol-1, and ΔC̊p,2a = -261 ±12 J-K-1-mol-1.