Experimental Determination of Equilibrium Constants of Copper Complexes in Aqueous Environment

Abstract

Abstract The experimental determination of equilibrium constants is required to estimate concentrations of reagents and/or products in environmental chemical reactions. For an example, the choice of copper (Cu) complexation reactions was motivated by their fast kinetics and the ease of measurement of Cu by an ion‐sensitive electrode. Each individual titrant of sulfate (SO 42‐ ) and oxalate (C 2 O 42‐ ) was expected to have its own unique characteristics, depending on the bonding in Cu‐ligands connected to the aqueous species. The complexation reaction of Cu with SO 42‐ somewhat fast reached equilibrium status compared with C 2 O 42‐ . The experimental equilibrium constants (K eq ) of copper sulfate (CuSO 4 ) and copper oxalate (CuC 2 O 4 ) were determined 10 2.2 and 10 3~4.3 , respectively. Key Words : Equilibrium constants, Copper (Cu), Complexation reaction, Cu-ligands, Sulfate (SO 42- ), Oxalate (C 2 O 42- ) 1) 1. Introduction Equilibrium constants have been measured for metal complexes in water system due to their importance in environmental chemistry. In general, chemical reactions move towards a dynamic equilibrium in which both reactants and products are present but have no further tendency to undergo net change (Atkins and Paula, 2005). Due to this phenomenon, both reactants and products have the significant concentrations in the equilibrium mixture. Equilibrium constants for chemical reactions can be computed from thermodynamic data. However, if thermodynamic data are unavailable for a particularly environmental chemical reaction, they can be estimated experimentally (Brewer and Baughman, 2004). Equilibrium constants can be determined by