Hello candidate,

The estimation of hardness the use of EDTA and metal ion is based on the method of  complexometric titration.

The basic process of determination is by titrating with a standard solution of ethylene diamine tetra acetic acid (EDTA) which is a complexing agent. Since EDTA is insoluble in water, the disodium salt of EDTA is taken for this experiment.

Hope That this information was helpful for you.

Good luck!!