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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

Full paper is available at

DOI: 10.2478/s11696-009-0027-5


Chemical Papers 63 (4) 420–425 (2009)

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