Lecture - 20 Complexometric Titrations.pptx

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1. Complexometric Titrations Lecture - 20 Subject – Pharmaceutical Analysis-I Course – B. Pharm 1 st Year Faculty Name – Umesh Kumar

2. Important terms; Complexometric titration:  A titration based on the formation of coordination complexes between a metal ion and complexing agent (or chelating agent) to form soluble complexes . Complexometric indicator:  water soluble organic molecules that undergoedefinite colour change in the presence of specific metal ions and are used incomplexometric titrations. Complex:  a substance composed of two or more components capable of an in- dependent existence. Complexation :  the association of two or more chemical species that are capable of independent existence by sharing one or more pairs of electrons.

3. Complexometric titration: Complexometric titration is a form of volumetric titration in which the formation of a colored complex is used to indicate the end point of a titration . Complex-forming reactions involving many metal ions can serve as a basis for accurate and convenient titrations for such metal ions . These kinds of complex ion titration procedures referred to as complexometric titrations, have high ac- curacies and offer the possibility of determinations of metal ions at the millimole levels. Although this type of a chemical reaction can be classified as a  Lewis acid-base reaction , it is more commonly known as a  complexation reaction .

4. Conti…….. As applied to chemical analysis, this definition is generally taken to mean the bonding of a central metal ion, capable of accepting an unshared pair of electrons with a ligand that can donate a pair of unshared electrons. In a complexation reaction, the product of the reaction is termed a  complex . The species which donates the electron pairs by acting as a  Lewis base  is known as a  complexing  agent or ligand , and the ion which accepts the donated electrons, the Lewis  acid , is called the  central ion or central atom .

5. EthyleneDiamineTetraAcetic acid EDTA called as ethylenediaminetetraacetic acid is a complexometric indicator consisting of 2 amino groups and four carboxyl groups called as Lewis bases. Edta is a hexadentate ligand because of its competence to denote six pair of lonely electrons due to the formation of  covalent bonds . Even the presence of small metal ions would lead to a distinct change in the color . This leads to the formation of a weak complex.

6. Conti……. Complexing agents are less soluble in water, and most of them are free acids. They are used in volumetric Solutions. Before using them, they are converted into sodium salts that are feasible in water. Since they are characterised with less solubility in water, they are used for titration. Sometimes simple titration methods are used to determine the simple metal ions present in water. But to determine the exact number of metal ions present complexometric titration is used, and it is conducted using EDTA.

7. Conti…….. To be continued in Next video