Complexometric or chelateometry titration is a type of volumetric analysis in which the formation of a colored complex is used to detect the titration’s endpoint. This type of titration is very effective for determining the concentration of a mixture of metal ions in the sample solution. The endpoint of the titration is usually detected using an indicator capable of producing a recognizable color change.
EDTA (ethylenediaminetetraacetic acid) is an aminopolycarboxylic acid that is a colorless, water-soluble solid. It has four carboxyl groups and two amine groups that can all act as electron pair donors or Lewis bases. etheylenediaminetetraacetic acid (EDTA) is a hexadentate ligand since it can donate its six lone pairs of electrons to form coordination covalent connections with metal cations.
Why is it necessary to standardize solutions of EDTA in complexometric titrations?
To determine the exact concentration (molarity or normality) of the prepared solution of EDTA it needs to be standardized before titration of the analyte. In a titration reaction, a known volume of titrant of known concentration (A) is added to an unknown quantity of reactant (B). We cannot calculate the molar equivalence without knowing A or B.
For example,
Metal ion + EDTA→ (Metal ion) EDTA.
Because [metal ion] + is unknown, there is no way to determine the amount present unless we know [EDTA] well. Therefore, to standardize and calibrate the titration, a known mass of primary standard is necessary.
Several reagents such as metallic magnesium, calcium carbonate, and metal bismuth can be used to standardize EDTA. Standardize the EDTA solution against the same cation and use the same method that can be used during sample analysis for optimal results.
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