Solubility Determination of Ammonium Dihydrogen Phosphate in Four Binary Solvents at Different Temperatures of 283.15–323.15 K, as well as Correlation, Solvent Effects, and the Inorganic Salt-Induced Liquid–Liquid Phase Separation Phenomenon

The mole-fraction solubility of ammonium dihydrogen phosphate (MAP) in four binary solvent systems: water + n-propanol, water + i-propanol, water + tert-butanol, and water + acetone, was determined by the gravimetric method at atmospheric pressure and temperatures ranging from 283.15 to 323.15 K. It was found that the solubility of MAP increased with increasing temperature and with the mole fraction of water in the binary solvent systems. In this study, the structural characteristics and intermolecular interactions of MAP molecules were analyzed by using the molecular electrostatic potential surface (MEPS) and Hirshfeld surface (HS). Correlation analysis of the experimental solubility data was carried out by the modified Apelblat equation, the van’t Hoff equation, the λh equation, and the Jouyban–Acree model. The relative deviation, mean relative deviation, and root-mean-square deviation were also calculated. The analysis results showed that the modified Apelblat equation was the best correlation model. At the same time, this study also provides a reasonable explanation for the phenomenon of inorganic salt-induced liquid–liquid phase separation in the experiment.