In a complexometric titration of metal ion with ligand $M ($ Metal ion $)+ L ($ Ligand $) \rightarrow C ($ Complex $)$ end point is estimated spectrophotometrically (through light absorption). If 'M' and 'C' do not absorb light and only 'L' absorbs, then the titration plot between absorbed light
( $A$ ) versus volume of ligand 'L' $(V)$ would look like
Ligand concentration is maximum when the reaction has not been initiated.
At that point, absorption of light by ligands will be maximum.
As the reaction starts, ligand concentration decreases so is the absorption of light till the point where all the metal ions are consumed and further complex formation does not take place.
A coordination compound holds a central metal atom or ion surrounded by various oppositely charged ions or neutral molecules. These molecules or ions are re-bonded to the metal atom or ion by a coordinate bond.
Coordination entity:
A coordination entity composes of a central metal atom or ion bonded to a fixed number of ions or molecules.
Ligands:
A molecule, ion, or group which is bonded to the metal atom or ion in a complex or coordination compound by a coordinate bond is commonly called a ligand. It may be either neutral, positively, or negatively charged.
