Solubility of calcium oxalate in 1-alkanols and ethanol--water mixtures

Solubility profiles for calcium oxalate were determined in pure 1-alkanols and ethanol--water mixtures at 20 degrees. The magnitude of solubility in the aliphatic alcohols was highest in methanol and decreased in a nonlinear fashion as the dielectric constant decreased, going to n-decanol. In ethanol--water mixtures, the solubility increased nonlinearly with water content or increasing dielectric constants. The work factor for these systems was also calculated and, as expected, a "mirror image" to the solubility profiles was evidenced. In the mixed solvent system, a dramatic change in the magnitude of solubility occurred after a dielectric constant value of about 60, indicating ionic association or ion-pairs below this value. The Born relationship of solubility and ionic size was tested in the ethanol--water system, and the ionic size of the divalent species of about 2.27 A agreed with the theoretical ionic size of about 2.4 A. These results indicate that the water number of calcium is 8 or that a monolayer of dipoles surrounds this divalent cationic species.