Complexometric or chelatometric titration is a type of volumetric analysis in which the formation of a colored complex indicates the endpoint of a titration. Complexometric titrations are particularly useful for determining different metal ions. Direct, back, and replacements are types of complexometric titrations that are used for a variety of applications.
Why do we use EDTA in total hardness analysis of water?
Ethylenediaminetetraacetic acid (EDTA) is used to determine the total hardness concentration, as EDTA is capable of complexing with numerous metals in an ionic form that occurs in the water body. Using EDTA, the total hardness of water is determined mainly in terms of calcium carbonate (CaCO3) and magnesium carbonate (MgCO3), as these compounds are present in the highest amounts.
Using EDTA as the titrant, we titrate a water sample to quantitatively evaluate the total hardness of the water. This means that EDTA is poured drop-by-drop from the burette until the color of the indicator indicates the perfect endpoint of the reaction. Typically, an Eriochrome black T (EBT) indicator is used to determine the endpoint.
With the addition of a buffer solution with a pH of 10, fully deprotonated EDTA complexes with all metals at the end-point, to ensure that the EDTA has been completely deprotonated to complex with the various metal ions responsible for the hardness of the water. The ratio of the complexed metal to the fully deprotonated EDTA is 1, therefore stoichiometric calculations are conducted, which are simple to perform.
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