Procedure for Complexometric Titration

Complexometric titration is a standard laboratory procedure.

Complexometric titration, a type of volumetric analysis, uses a colored complex to indicate a reaction's end-point, often to determine the proportion of metal ions in a mixture.

Ligands

Complexometric titration uses a chemical acting as a ligand in metal complex ions to determine the metal ion concentration. Ethylenediaminetetraacetic acid, or EDTA, often serves as the ligand of choice.

Buffered Reaction Solution

A precisely measured volume of an unknown solution containing metal ions goes into a conical flask. A buffer solution, usually added to maintain optimum pH, ensures completion of the complex formation of the metal ions with EDTA. Dilution with distilled water achieves the optimum concentration for observing the color change.

The Indicator

A dye added to the mixture at this stage provides the color needed for observing the end-point. Eriochrome Black T, a suitable indicator, has a wine-red color when complexed with metal ions, but appears blue when free in solution.

Titration With EDTA

A known concentration of EDTA solution is used in the burette, and titrated against the reaction mixture containing metal ions. EDTA binds preferentially to metal ions, removing them from dye complexes. The end-point occurs when all metal ions have been complexed with EDTA, and the solution contains only free dye molecules, creating a color change.

References

• Truman State University Chemlab Guide: Determination of Mg by Titration with EDTA