A Review of Sodium Oxalate Solubility in Water

The solubility of disodium oxalate is important to many industries. This study compiled and statistically assessed the disodium oxalate solubility data available between 273 and 373 K. Sixty-six measurements were found from 19 studies. Two additional studies published their data graphically. The solubility was found to be an approximately linear function of the temperature, increasing about 0.0027 mol/kg per K. The coefficient of determination (R-2) of a linear fit to the data was 0.98. The mean measured solubility at 298.15 K was 0.274 mol/kg, with a standard error of 0.0026, with good agreement across data sets. The data were compared to calculated solubilities using a previously published thermodynamic model and shown to have reasonable agreement. The solubility of disodium oxalate was less than other alkali oxalates. Oxalate has a -2 charge, or -0.5 charge per oxygen, and an average bond valence of -0.17 per coordinating cation. Disodium oxalate is less soluble than other alkali oxalates because Na+ has a more closely matching opposite bond valence (0.16) than do other alkali cations. This is consistent with Brown's theory that the most stable solids are those where cation and anions have matching opposite bond valence without having to adjust to uncommon bond lengths or coordination numbers.