The Complex Formation of the Copper(II) Ion with Ethylenediaminetetraacetic Acid and N-(2-Hydroxyethyl)ethylenediamine-N,N′,N′-triacetic Acid

Abstract The complex formation of the Cu(II) ion with ethylenediaminetetraacetic acid (EDTA) and N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA) has been studied potentiometrically and polarographically over the wide pH range from 1 to 11 in aqueous solutions containing 1.0 mol dm−1 NaClO4 at 25.0 °C. Both the emf data obtained by potentiometric titrations and the pH-dependence of reversible half-wave potentials were explained in terms of the formation of the following complex species: for the Cu–EDTA complexes, CuL2− (logβ101=17.28±0.04), CuHL− (logβ111=20.15±0.04), CuH2L(logβ121=22.73±0.04), CuH3L+(logβ131=24.12±0.04), and CuH−1L3− (logβ1−11=6.83±0.05); for the Cu–HEDTA complexes, CuL− (logβ101=16.30±0.05), CuHL (logβ111=18.76±0.04), CuH2L+ (logβ121=19.85±0.04) and CuHL−1L2− (logβ1−11=6.35±0.05), where βpqr=[CupHqLr]/[Cu2+]p[H+]g[L]r, and where L denotes the unprotonated molecule of EDTA or HEDTA.