Which compound is commonly used to assess the hardness of water?

The use of EDTA (ethylenediaminetetraacetic acid) is prevalent in the assessment of water hardness due to its ability to effectively sequester calcium and magnesium ions, which are the primary contributors to water hardness. When water samples are tested, EDTA forms stable complexes with these metal ions, allowing for accurate quantification of water hardness. This complexation reaction is integral in titration procedures, where the endpoint can be visually determined through an indicator that changes color once all hardness ions have reacted with the EDTA.

Other compounds mentioned, such as sodium sulfate, calcium carbonate, and magnesium chloride, do not serve the same purpose as EDTA in the context of measuring water hardness. Sodium sulfate, for instance, does not interact specifically with hardness ions in a way that facilitates measurement. Calcium carbonate and magnesium chloride are involved in the composition of hard water but do not provide a method for assessing hardness themselves. Thus, EDTA stands out as the correct choice for determining water hardness in laboratory settings.