Speciation of 2-Hydroxybenzoic Acid with Calcium(II), Magnesium(II), and Nickel(II) Cations in Self-Medium.

Equilibriaoccurring between 2-hydroxybenzoic acid (salicylic acid,H2L) and calcium(II), magnesium(II), and nickel(II) havebeen studied by potentiometric titrations with glass electrodes at298.15 K in self-medium constituted of 1.05 mol·kg–1NaHL. The self-medium composition can be considered constant sinceonly a small amount of ligand HL–is transformedin the reaction products. The hydrogen ion concentration was variedfrom 10–2mol·kg–1to incipientprecipitation of a basic salt of each metal, whose formation dependson the particular metal. The total metal concentration, CM, ranged from 3.05·10–3mol·kg–1to 10.01·10–3mol·kg–1. The higher CMvaluewas imposed in order to avoid changes in the ionic medium and in theactivity coefficients. The experimental data have been explained byassuming the formation of the complexes: CaL; MgL, MgL22–, and MgL34–; NiLand NiL22–. [ABSTRACT FROM AUTHOR]