Open AccessSolubility of CaHPO4 2H2O in the quaternary system Ca(OH)2-H3PO4-NaCl-H2O at 25 C
Author(s) -
Paras R. Patel,
Thomas Grégory,
W. E. Brown
Publication year - 1974
Publication title -
journal of research of the national bureau of standards. section a. physics and chemistry
Language(s) - English
Resource type - Journals
eISSN - 2376-5704
pISSN - 0022-4332
DOI - 10.6028/jres.078a.043
Subject(s) - solubility , solubility equilibrium , ion , chemistry , activity coefficient , thermodynamics , ionic bonding , inorganic chemistry , analytical chemistry (journal) , aqueous solution , chromatography , organic chemistry , physics
Solubility of CaHPO 4 · 2H 2 O was determined in the quaternary system Ca(OH) 2 - H 3 PO 4 - NaCl - H 2 O at 25 °C in the pH range 4.39-6.38; ionic strengths of the saturated solutions varied from 0.00485 to 0.545, Satisfactory constancy in the solubility product, ( K sp = [Ca 2 +] ⋅ [HPO 4 2 -] ⋅ γCa 2 +⋅ γHPO 4 2 -= 2.49 ± 0.05 × 10 - 7 mol 2 × 1 - 2) was obtained when (i) the ion activity coefficients, γ i , were calculated with the Debye-Hückel equation, log γ i = - A Z i 2 I / ( 1 + B α i I ) + 0.0626 I ; the value 0.0626 for the coefficient in the linear term was derived from the solubility data by utilizing a statistical procedure, and (ii) formation of an ion pairNaHPO 4 - was taken into account; a statistically derived value for the stability constant of this ion pair is 7.0 ± 2.4 1 × mol -1 . The ion pairNaHPO 4 - appears to have significant concentrations in physiological fluids.