Determination of Hardness of Water Using EDTA Method

Introduction

• Hardness can be determined using different methods.
• Focus of the session: EDTA method.

Methods to Determine Hardness

1. EDTA Method
   • Most widely used due to its effectiveness in determining water hardness.
   • Helps in identifying impurities causing hardness.
2. Ohana's Method
   • Not commonly used.
3. Soap Titration Method
   • Also not commonly used.

What is EDTA?

• Chemical Composition:
  • Contains CH2, CH2, and a nitrogen atom.
• Nitrogen's Stability:
  • Nitrogen requires eight electrons in its outer shell (octet).
  • Has three bonds and one lone pair, leading to stability.
• Hexadentate Ligand:
  • EDTA is a hexadentate ligand, meaning it can bind through six different sites.

Ligands and Coordinate Bonds

• Ligand Definition:
  • A structure that needs electrons and forms coordinate bonds with metal ions.
• Coordinate Bond:
  • Formed by sharing electrons, typically between a metal ion and a ligand.

Structure of EDTA

• EDTA has nitrogen and oxygen atoms that bind metal ions (e.g., Ca²⁺ or Mg²⁺).
• Forms stable chelate complexes with these ions.

Principle of EDTA Method

• Full Name: Ethylene Diamine Tetra Acetic Acid
• Structure includes:
  • Ethylene (2 carbons)
  • Diamine (2 amine groups)
  • Tetra (4 acetic acid groups)
• Commonly forms complexes with Ca²⁺ and Mg²⁺ in water samples.
• Titration with Na2EDTA under pH 10 using EBT indicator.

EBT Indicator

• At pH 10, EBT indicator forms a wine-red colored complex with Ca²⁺ and Mg²⁺ ions.
• Color Change Mechanism:
  • Pure water: No reaction, EBT remains blue.
  • In hard water: EBT reacts, turning wine red.
  • During titration with EDTA: Color changes from wine red to blue, indicating completion of the reaction.

Summary of Reaction Steps

1. EBT (blue) + Ca²⁺ or Mg²⁺ -> Wine red unstable complex.
2. Upon titration with EDTA, the colorless stable complex forms, releasing blue EBT.

Conclusion

• Overview of EDTA's chemical structure and its role in determining water hardness.
• Significance of using the EDTA method for hardness detection.
• Encouragement to stay tuned and subscribe to Ekeeda for more content.