Complexometric Titration

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EDTA titration of Ca2+ requires buffer to maintain pH around:

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1. **EDTA Nature**: Ethylene Diamine Tetra-acetic Acid ($EDTA$) is a polyprotic acid that coordinates with metal ions as a hexadentate ligand.
2. **Protonation**: At low $pH$, the carboxylate groups are protonated ($COOH$), making $EDTA$ a poor ligand.
3. **Stability**: The complex formed with $Ca^{2+}$ ions is most stable in a basic medium.
4. **Buffer Choice**: An ammonium buffer ($NH_4Cl + NH_4OH$) is typically used to maintain a **$pH$ of approximately $10$**.
5. **Indicator**: Under these conditions, Erio-chrome Black T ($EBT$) works effectively to signal the endpoint.

Complexometric Titration

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