Complexometric Titration

Introduction

• Discussion on the principle of complexometric titration.
• Example involving calcium and magnesium ions.

Principle of Complexometric Titration

• Indicator Used:
  • Eriochrome Black T (EBT)
    • Other names: Modern Black T, Solucrome Black T.
• Process:
  • Calcium and magnesium ions are present in the sample.
  • Add EBT indicator, forming a complex with these ions which results in a wine red color.
  • Titrate with EDTA (Ethylenediaminetetraacetic acid), a complexing agent.

Reaction Details

• After Titration:
  • All calcium and magnesium ions react with EDTA.
  • Formation of chelate (complex) with EDTA.
  • EBT indicator is released, changing color to blue.
• Final Color:
  • Initial color: Wine red → Final color: Blue.

Overview of Complexometric Titration

• A type of volumetric analysis.
• Fixed volume of sample/analyte is titrated with EDTA.
• Allows calculation of metal ion concentration.
• Mainly used for the detection of metal ions.

Complexing Agents Used in Complexometric Titration

1. EDTA (Ethylenediaminetetraacetic acid)
   • Commonly used in laboratories, sodium salt form prevalent.
2. DTPA (Diethylenetriaminepentaacetic acid)
3. EGTA (Ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid)
4. Ammonia
   • Sometimes used as a complexing agent.
5. Ethylenediamine
   • Occasionally used for complex formation.

Structures of Complexing Agents

• EDTA: [ H_2N-CH_2-C(=O)O-CH_2-NH-CH_2-COOH ]
• DTPA: [ H_2N-(CH_2)_2-NH-(CH_2)_2-NH-(CH_2)_2-COOH ]
• EGTA: [ H_2N-CH_2-CH_2-O-CH_2-CH_2-NH-COOH ]
• Ammonia: [ NH_3 ]
• Ethylenediamine: [ NH_2-CH_2-CH_2-NH_2 ]_

Summary of Complexing Agents

• EDTA: Hexadentate ligand, forms six bonds with metal ions.
• DTPA: Octadentate ligand, forms eight bonds.
• Ammonia: Monodentate ligand.
• Ethylenediamine: Bidentate ligand, forms two bonds.

Conclusion

• Disodium EDTA is primarily used in complexometric titration in the laboratory.