Estimation of Hardness of Water

Complexation Reaction: $$\text{Ca}^{2+} / \text{Mg}^{2+} + \text{EDTA}^{4-} \longrightarrow [\text{M(EDTA)}]^{2-} \quad (\text{Highly Stable Chelate Complex})$$

Concept: Hardness in water due to calcium and magnesium ions is quantitatively estimated via complexometric titration using a standard solutions matrix of disodium salt of EDTA, utilizing indicators like Eriochrome Black T (EBT) under buffered alkaline conditions.

Notation:

• $$\text{EDTA}^{4-}$$ = Ethylenediaminetetraacetate ion (a powerful hexadentate chelating ligand);
• $$[\text{M(EDTA)}]^{2-}$$ = Thermodynamically stable, soluble metal-EDTA chelate.