Stability of the calcium dioxalate complex.

: The stability constant of the calcium dioxalate complex Ca(C2O4)2(2-), was measured at 38 C by examining the solubility of [45CA]whewellite in solutions with various oxalate concentrations. The solubility data showed that when oxalate was present above 10 mM increasing the oxalate concentration caused an increase in the apparent solubility of whewellite. This phenomenon was analyzed in the context of ionic equilibrium equations, and the stability constant of the dioxalate complex was estimated by fitting the experimental data with a nonlinear least-squares program. The estimated thermodynamic stability constant of the calcium dioxalate complex is 17.32 +/- 1.1 M-1.