In the hardness test, what is the titrant used?

In the hardness test, EDTA (Ethylenediaminetetraacetic acid) is used as the titrant because it is a chelating agent that forms stable complexes with metal ions, particularly calcium and magnesium, which are primarily responsible for water hardness. The reaction between EDTA and these metal ions allows for an accurate determination of their concentrations in the water sample. During the titration process, as EDTA is added to the solution, it binds to the calcium and magnesium ions, effectively removing them from solution.

The endpoint of the titration is indicated by a color change, typically facilitated by a suitable indicator. This color change signifies that all of the hardness-causing ions have reacted with the EDTA. The amount of EDTA used correlates directly to the concentration of hardness in the water, allowing for precise quantification.

Other options like sodium chloride, calcium carbonate, and magnesium sulfate do not serve the role of a titrant in hardness testing. Sodium chloride is primarily used as a supportive ion and does not complex with hardness ions. Calcium carbonate and magnesium sulfate are actual components of water hardness rather than titrants used in the analytical method for determining hardness levels. Thus, EDTA stands out as the appropriate choice for this