Thermodynamic Properties of NaH2PO4⋅2H2O and K2HPO4⋅3H2O Crystal Hydrates

Abstract NaH 2 PO 4 ⋅2H 2 O and K 2 HPO 4 ⋅3H 2 О crystal hydrates are synthesized from aqueous solutions at room temperature. The resulting samples are identified using X-ray structural analysis (XSA) and thermogravimetry (TG). The enthalpies of dissolution in water at 298.15 K are determined through the calorimetry of dissolution, and the standard enthalpies of formation for the crystal hydrates of sodium dihydrophosphate and potassium hydrophosphate are calculated. A comparison of the estimated and experimentally obtained values of the enthalpy of formation for NaH 2 PO 4 ⋅2H 2 O and K 2 HPO 4 ⋅3H 2 О shows they are within the limits of the error of determination.