Question

Why is it necessary to standardize solutions of EDTA in complexometric titrations?

Answer 1

The development of a coloured complex is employed to identify the end point of a titration in complexometric titration, which is a type of volumetric analysis. Complexometric titrations are very effective for determining the concentration of a combination of metal ions in solution. The end-point of the titration is generally detected using an indicator that produces an unmistakable colour shift. The processes in which a simple ion is converted into a complex ion and the equivalence point is measured using metal indicators or electrometrically are known as complexometric titrations.

Complete answer:
Ethylenediaminetetraacetic acid (EDTA) has four carboxyl groups and two amine groups, all of which can serve as electron pair donors or Lewis bases. EDTA is a hexadentate ligand because it can possibly donate its six lone pairs of electrons to form coordinate covalent connections with metal cations. In practise, however, EDTA is only partly ionised, forming fewer than six coordinate covalent connections with metal cations.
In a titration reaction, I a KNOWN volume of titrant is supplied to an unknown quantity of reactant of (ii) known concentration. The analyst cannot calculate molar equivalency without knowing I or (ii).
To put it another way, you're doing the following:
$Metal\text{ }ion+EDTA\to \left( Metal\text{ }ion \right)\cdot EDTA.$
Because ${{\left[ Metal\text{ }ion \right]}^{+}}$ is unknown, there is no way to estimate the amount present unless you know $[EDTA]$ pretty well. To standardise and calibrate the titration, a known mass of primary standard is necessary.
Disodium EDTA is widely used to standardise transition metal cation aqueous solutions. At pH values below 12, disodium EDTA only forms four coordinate covalent connections to metal cations. The amine groups stay protonated in this pH range, making them unable to give electrons to the creation of coordinating covalent bonds. Note that every species of EDTA may be represented by the shorthand notation $\mathbf{N}{{\mathbf{a}}_{\mathbf{4}-\mathbf{x}}}{{\mathbf{H}}_{\mathbf{x}}}\mathbf{Y}$ , with x being the amount of acidic protons bound to the EDTA molecule.
${{M}^{2+}}~+\text{ }{{H}_{4}}Y\text{ }\to \text{ }M{{H}_{2}}Y\text{ }+\text{ }2{{H}^{+}}$

Note:
EDTA is primarily used in industry to sequester metal ions in aqueous solutions. It prevents metal ion contaminants from changing the colour of coloured goods in the textile industry. EDTA prevents metal ions, particularly $M{{n}^{2+}}$ , from catalysing the disproportionation of hydrogen peroxide, which is utilised in chlorine-free bleaching, in the pulp and paper sector. EDTA is used as a preservative or stabiliser in some foods to avoid catalytic oxidative decoloration, which is catalysed by metal ions.