In this pH range, the amine groups remain protonated and thus unable to donate electrons to the formation of coordinate covalent bonds.
For most purposes it can be considered that the formation of the metal cation-EDTA complex goes to completion, and this is chiefly why EDTA is used in titrations and standardizations of this type.
The experimental points are plotted as per Beer’s law: A= E*c*l where E= molar extinction coefficient and l= optical path length usually 1 cm.
To carry out metal cation titrations using EDTA, it is almost always necessary to use a complexometric indicator to determine when the end point has been reached.
Color change shows that the indicator has been displaced (usually by EDTA) from the metal cations in solution when the end point has been reached.