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.
• 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
• 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
• 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
• 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.
• 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
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...