Complexometric titrations (key words: EDTA) & Stability with respect to pH of some metal-EDTA complexes

This particular experiment is concerned with the way in which complexation reactions can be employed in titrimetry, especially for determining the proportions of individual cations in mixtures.

Theory

Ethylenediaminetetraacetic acid (EDTA) is the most widely used complexing agent in Complexometric titrations.

The pKa values for EDTA are pKa1 = 2.0, pKa2 = 2.7, pKa3 = 6.2 and pKa4 = 10.3 at 20 degrees Celsius.
These values suggest that it behaves as a dicarboxylic acid with two strongly acidic hydrogens. Na2H2Y.2H2O is most commonly used in the preparation of EDTA solution because of its high solubility.

The molecule has six potential sites for co-ordination and forms 1:1 complex with most metal ions.

water and posses almost the same colors as aqueous metal ion.

The metal complexes are soluble in It is obvious from this equation that the stability of the complex is dependent upon the pH of the medium etc. therefore EDTA titrations are generally carried out in buffered media.


Stability with respect to pH of some metal-EDTA complexes