The association constants of strontium ion with pyrophosphate ions in aqueous solution

Abstract

The determination of equilibrium free (uncomplexed) metal ion in the presence of complexing agents is critical in the evaluation of association constants. In this study equilibrium free strontium ion concentration has been evaluated by determining the strontium ion distribution between a cation exchange resin and aqueous solution with the help of radiotracer Sr90 in the absence and in the presence of complexing agent pyrophosphate ion. The association constants have been determined for a 1:1 Sr2+-P2O7 4- complex at 25°C, pH=10.0, and at various ionic strengths. The log K values at different ionic strengths studied are: Ionic Strength log K 0.10 5.35 + 0.18 0. 25 4.50 + 0.05 0.50 3.97 + 0.13 0.75 3.78. -+ 0.20 The log K values indicate that strontium is strongly bonded to the pyrophosphate ion and the variation of log K with the ionic strength is as expected for this type of system.