Solubility of CaHPO4 2H2O and formation of ion pairs in the system Ca(OH)2 - H3PO4 - H2O at 37.5 C

摘要: The solubility isotherm for CaHPO4 · 2H2O (DCPD) in the three-component system Ca(OH)2 - H3PO4 H2O was determined pH range 3.5 to 6.8 by leaching a thermostated column of DCPD with dilute phosphoric acid solutions. In confirmatory experiments, equilibrium approached both from super- and under-saturation shaking appropriate calculated ionic activity product (Ca++) × ( HPO4= ), appeared be parabolic function minimum near 5.0. dependence could accounted considering ion pairs [CaHPO4]° [CaH2PO4]+ as semi-empirical parameters. Under condition saturation respect DCPD, pair must constant. species shown vary directly hydrogen activity. activities two were adjusted give set pH-independent products mean 2.19±0.011 10-7. stability constants are 5.88±0.031 102 7.49 ±0.039, respectively. Experiments conducted study hydrolysis more basic calcium phosphates kinetics these transformations is discussed. significance human serum considered.