Titration involves the conversation of simple metal ion to complex ion by addition of reagent are called as Complexometric titration. The complex formed is water soluble and stable in nature.
In complexometric titration, metal ion accepts electron and the species donates electrons which are called as ligand. Commonly used ligand in complexometric titration is EDTA – ethylene diamine tetra acetic acid or Na EDTA – disodium salt of EDTA.
Indicator used in complexometric titration is called as metal indicator. They give one color in presence of metal ions and gives different color in absence of metal ions.
Example:
Solochorme black T
Modrant balck T
Variamine blue
Muxeride
In complexometric titration, first metal ion reacts with indicator and forms metal-indicator complex. Then EDTA is added which reacts with metal ion to form metal-EDTA complex which is more stable then metal-indicator complex. So later metal-indicator complex breaks and gives free metal ions to react with EDTA. At equivalent point, free metal ions are not present and thus free indicator ion gives a color which is different from the color of metal-indicator complex.
Application of Complexometric titration:
For determining various metals like Ca, Mg, Zn, Pb, Fe, Al, Mn etc present in official pharmaceutical preparations.
For determining hardness of water