eng Science and Education Publishing World Journal of Chemical Education 2375-1657 2015-02-09 3 1 5 21 10.12691/wjce-3-1-2 WJCE2015312 article Maria Michela SALVATORE frsalvat@unina.it 1 Francesco SALVATORE 1 Dipartimento di Scienze Chimiche, Universite degli Studi di Napoli 'Federico II', Via Cintia, 21 - 80126 Napoli, Italy In spite of the apparent technical simplicity with which visual complexometric titrations of metal cations with aminopolycarboxylic acids titrants are performed, a complex chemistry takes place in the titrated solution during the titration, due to the chemical environment and to the insuppressible chemical properties of metal cations, aminopolycarboxylic acids and metallochromic indicators. This chemical complexity makes rigorous exposition and evaluations of complexometric titrations arduous. Nonetheless, by the introduction of the notions of groups of chemical species and reactions between groups of chemical species (with the connected concept of conditional formation constant), a frame is created within which complexometric titrations with aminopolycarboxylic acids can be collocated and which allows a reasonably simple presentation and evaluation of the analytically relevant aspects of this type of titrations. In a sense, the well known concept of conditional complex formation constant is updated in a way that facilitates understanding and use. http://pubs.sciepub.com/wjce/3/1/2/wjce-3-1-2.pdf aminopolycarboxylic acids complexometric titrations conditional formation constant EDTA magnesium Eriochrome Black T water hardness