Thermodynamic Behavior of the System Water/d-Sucrose/NH4H2PO4 at 298.15 K, and Salting-Out of NH4H2PO4 on d-Sucrose Solutions

The hygrometric method is used to determine new thermodynamic data on water activity and saturated aqueous solution of the water/d-sucrose/ammonium dihydrogen phosphate (ADP) system in a wide range of NH₄H₂PO₄ molality, ranging from 0.1 to 3 mol⋅kg⁻¹, and for various d-sucrose contents from 0 to 4 mol⋅kg⁻¹. Powder X-ray diffraction (XRD) and attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy were used to characterize the solid state. The Pitzer–Simonson–Clegg model (PSC) is used to fit the experimental data of osmotic coefficient obtained from water activities data. The predicted saturated aqueous solutions, with the PSC model, are in good agreement with experimental data. For the concentration inferior to 1 mol⋅kg⁻¹, the negative deviation from ideality was shown with increasing the ADP concentrations. The estimated values of the activity coefficient of d-sucrose, activity coefficient of ADP, and the Gibbs energy of transfer of ADP from water to mixture (water/d-sucrose) show that both ADP and d-sucrose exert significant salting-out effects on the aqueous solution.