Notes on Titration

Topics: Ligand, Coordination chemistry, Atom Pages: 3 (325 words) Published: January 22, 2011
Titration Topics to be discussed: • Complex ions & ligands. • EDTA in complexometric titration. • Indicators for complexometric titration. • Titration curve • Application of complexometric titration. 1

Complexometric titration method
• An analytical method involving complex formation reactions. • A complex ion (or coordinate complex) is formed from electron donating compound & a metal ion.


Coordination Complex
• The electron donating compound is a neutral organic molecule or anion.

• For a coordination complex, the metal ion is called the centre atom. • The molecule or anion is called the ligand and are electron donating groups. 3

Coordination Complex
• A ligand can have several sites that bind to the centre atom (cation) – multidentate ligand, e.g. monodentate, bidentate,tridentate etc. • The coordination number of the cation shows the number of covalent bonds formed with the electron donating groups. 4

Coordination Complex
• The usual coordination number is two, four and six (WHY??) • The complex formed can be positive, negative charge or neutral. A complex ion

Centre ion Ligand

Coordination complex
• E.g. of complexes with a coordination number of four are:


positive charge, ammonia ligand is unidentate.

Cu(NH2CH2COO)2 neutral, the ligand
glycine is bidentate.


negative charge, ligand chloride is unidentate.

Coordination complex
• In the analysis using the method complexometric titration, chelate type of coordination complex is used. • A chelate is a complex that formed from a metal ion and two or more groups of donors in one ligand. 7

Example of chelates

Complex copper(II) glycinate: Two glycine ligands, two donors in each ligand 8

Chelate EDTA

Ligand ethylenediaminetetraacetic acid (EDTA): One ligand, six donor groups can form a chelate 9

Chelates in the Environment
• Example: Tannic Acid • From leaves of trees, present...
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