Solubility and Complex-Ion Equilibria

Solubility and Complex-Ion Equilibria broadens the previous chapter’s coverage of equilibria to include aqueous systems containing two or more solutes of slightly soluble ionic compounds and the formation of metal complexes in solution. Solubility equilibria which allow quantitative predictions of how much of a compound will dissolve under given conditions are covered. The meaning of the solubility product constant (K sp) and how to calculate it from molar solubility values is presented. Also discussed is determination of molar solubility from K sp. Calculations demonstrate how to predict the formation of a precipitate by comparing the ion product or solubility quotient (Q) with K sp. Formation constants of complex ions and calculations involving complex ion equilibria are explained.

Accuracy of Molar Solubility Prediction from Hansen Parameters. An Exemplified Treatment of the Bioantioxidant l-Ascorbic Acid

Estimating molar solubility from the Hildebrand-Scott relation employing Hansen solubility parameters (HSP) is widely presumed a valid semi-quantitative approach. To test this presumption and to determine quantitatively the inherent accuracy of such a solubility prognosis, l-ascorbic acid (LAA) was treated as an example of a commercially important solute. Analytical calculus and Monte Carlo (MC) simulation were performed for 20 common solvents with total HSP ranging from 14.5 to 33.0 (MPa)0.5 utilizing validated material data. It was found that, due to the uncertainty of the material data used in the calculations, the solubility prediction had a large scattering and, thus, a low precision. Prediction power is most adversely affected by the uncertainty of the HSP estimates (solvent and solute), followed by the solute heat of fusion. The solute melting temperature and molar volume have minor effects. Computed and experimental solubilities show the same qualitative behavior, while quantitative discrepancies reach one to three orders of magnitude. Solubility estimates were found to provide, at best, rough guiding information but, with the quality of material data on LAA available, they cannot be rated semi-quantitative. It is assumed that these results generally apply at least to solute-solvent systems with a material data quality and solubility similar to LAA.

Determination of Thermodynamic Parameters from the Dissolution of Strontium Hydroxide in Water and Mixed Solvent Systems by pH-Metric Method

In this study, saturated solutions of Sr(OH)2 in pure water and in mixed solvent systems (methanol - water, ethanol - water, 1-propanol - water, and 2-propanol - water) at two temperatures were prepared and titrated with standard HCl solution by using pH metry. Using these titration data, the molar solubility (s), solubilty product (Ksp) and Gibbs free energy (Go), entropy change (ΔSand#176;) and enthalpy change (ΔHand#176;) for dissolution of strontium hydroxide was determined. At room temperature (20and#176;C), the s, Ksp, ∆Go were found to be 4.28 x 10-2 mol L-1, 3.13 x 10-4 mol3L-3 and 19.70 kJ mol-1 respectively. The ΔHand#176; and ΔSand#176; of the reaction is 2.90 kJ mol-1 and – 60.80 J. mol-1 K-1. With increasing percentage content of organic solvent in mixed solvents, the molar solubility and Ksp decreased and ∆Go, ΔHand#176; and ΔSand#176; values increased. The results were correlated with the dielectric constant value of the solvents used in the study.

THE SOLUBILITY OF BERYLLIUM OXIDE IN AQUEOUS BERYLLIUM SULPHATE SOLUTIONS

It is observed that ignited beryllium oxide was soluble in concentrated aqueous solutions of beryllium sulphate to the extent of 1 mole of oxide per 2 moles sulphate, saturation being virtually complete within 6 hours at 80 °C. Since the molar solubility of aluminum oxide is much lower under similar conditions, it is suggested that partial resolution of oxide mixtures might be made on this basis.