• The assertion that EDTA (ethylene diamine tetraacetic acid) is used to determine the hardness of water is accurate. EDTA is a chelating agent, which means it forms stable complexes with metal ions by surrounding them with multiple coordinating groups. This property of EDTA makes it suitable for titrations used to determine the concentration of metal ions, including the ions responsible for water hardness.
• Water hardness primarily arises from the presence of calcium (Ca²⁺) and magnesium (Mg²⁺) ions in the water. These ions can interfere with the action of soaps and can lead to scale buildup in pipes and appliances. The hardness of water can be classified into two types: temporary hardness and permanent hardness. Temporary hardness is due to the presence of bicarbonate ions, while permanent hardness is caused by the presence of calcium and magnesium ions in forms other than bicarbonates.
• EDTA is commonly used to determine water hardness through a titration method called complexometric titration. In this process, a solution of EDTA is slowly added to a water sample containing metal ions. The EDTA forms stable complexes with the calcium and magnesium ions in the water. The endpoint of the titration is determined using an indicator that changes color when all the calcium and magnesium ions have been complexed by the EDTA. This color change indicates that the metal ions have been sequestered by the EDTA, effectively "softening" the water.

 

The balanced chemical reaction for the titration of calcium ions (Ca²⁺) with EDTA can be represented as follows:

Ca²⁺ + EDTA⁴⁻ → Ca-EDTA²⁻

• The stoichiometry of this reaction allows the determination of the concentration of calcium ions in the water sample, which can then be used to calculate the hardness of the water. Similar reactions occur for the complexation of magnesium ions.

 

Overall, EDTA is an essential reagent in the determination of water hardness due to its ability to form stable complexes with metal ions, allowing for accurate and reliable analysis of the calcium and magnesium content in water samples.

 

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