Solubilities in Aqueous Solutions of Ammonium Sulfate and Potassium Salts of Malonic, Succinic, or Glutaric Acid

The aqueous solubility of the least soluble salt was studied in mixtures of ammonium sulfate and one of the following organic acids in either a 1:1 or 2:1 ratio with KOH:malonic acid, succinic acid, and glutaric acid. Solubility temperatures were determined in solutions of known concentrations using differential scanning calorimetry. The identity of the least soluble solid was determined by a combination of X-ray crystallography and infrared spectroscopy. The identified solids were found to be potassium sulfate (19% of samples), ammonium sulfate (5% of samples), and compounds with varying ratios of NH₄⁺/K⁺ with SO₄^2- (76% of samples). The organic fraction of solutions appeared to have no impact on the identity of the least soluble solid but did have an impact on that solid's solubility in the respective solution. In general, the potassium-containing compounds were found to be less soluble than the analogous sodium-containing compounds previously reported.