Estimation of composition, coordination model, and stability constant of some metal/phosphate complexes using spectral and potentiometric measurements
Khalid Abu-Shandi and Fadel Al-Wedian
Department of Chemistry, Faculty of Science, Tafila Technical University, P. O. Box 179, Tafila, 66110, Jordan
Received: 31 May 2008 Revised: 1 November 2008 Accepted: 6 November 2008
Abstract: Complexation reactions in a binary metal/phosphate system were studied. Protolytic equilibria of phosphate in the presence
of cobalt, nickel, iron, copper, chromium and silver metal ions were investigated by potentiometric titrations in the pH range
of 2–11. Stability constants of the metal/phosphate complexes were determined by computer analysis of the potentiometric titration.
Potentiometric titrations suggest that the presence of metal phosphate and metal hydrogen phosphate provides the solutions
with stability constants logK
c 2.21, 2.11, 2.23, 2.34, 1.96, and 2.14 of Co, Ni, Fe, Ag, Cr, and Cu/phosphate, respectively. The results of infrared spectroscopy,
X-ray powder diffraction and equilibrium studies were used to reveal the mode of interaction between the metal ions and phosphate.
Metal phosphates with a hydrogen phosphate anion and fully nonprotonated phosphate could be isolated under the reaction conditions.
Keywords: phosphate - potentiometric titration - stability constants - infrared spectroscopy - X-ray powder diffraction
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Chemical Papers 63 (4) 420–425 (2009)