EDTA4- (ethylene diamine tetracetate ion) is a hexadentate ligand that can bind to the central metal ion by two nitrogen and four oxygen atoms. For most of the transition metals, EDTA4- forms very stable complexes. With most of the transition metals, this hexadentate ligand forms very stable complexes (usually octahedral structures). The two N atoms and the four negatively charged O atoms are the donor atoms in EDTA4-.
If the pH increases, EDTA salts are more soluble in water: the more EDTA is found in the salt form, the higher the pH of a water solution, and thus the greater the solubility of the room temperature. This can be accomplished by the incremental addition to the EDTA solution of a condensed sodium hydroxide solution.
The determination of water hardness by the EDTA process is one of the three primary methods for water hardness determination. EDTA stands for Ethylenediaminetetraacetic acid.
