Solid Liquid Equilibrium, Metastable Zone, and Nucleation Parameters of the Oxalic Acid−Water System

Measurements of the solubility and metastable zone for the oxalic acid−water system were obtained. The solubility was measured within the temperature range from 284.19 to 352.02 K. The mole fraction solubility was correlated satisfactorily with the temperature by the equation: x eq = 4 × 10 -7 e 0.0368 T . The values of enthalpy of dissolution, enthalpy of fusion, and enthalpy of mixing were determined to be 30.80, 58.158, and −27.358 kJ mol -1, respectively. The high value of enthalpy of mixing indicates a strong interaction between the solute and the solvent molecules. The width of the metastable zone was measured by an ultrasonic method and was correlated with the cooling rate and the equilibrium temperature by the equation: Δ T max = 7.2206 × 10 15 b 0.266 T eq -6.17 . The nucleation parameters of oxalic acid in water were determined from the metastable zone data. Over the equilibrium temperature range from 294.75 to 320.75 K, the nucleation rate constant was varied from 0.0084 to 0.0628 #/m 2 ·min, whereas the nucleation order was varied from 3.2419 to 2.8292. The obtained higher values of nucleation rate constant indicate a higher rate of nucleation. The role of the presence of small amounts of sulfuric acid on the metastable zone width was also investigated. The widest metastable zone was measured due to the presence of sulfuric acid at a concentration of 2.3 × 10 -9 g/g of solution.