Hardness in groundwater is due to the presence of metal ions, primarily Mg^2+ an

Question

Hardness in groundwater is due to the presence of metal ions, primarily Mg^2+ and Ca^2+. Hardness is generally reported as ppm CaC03 or mmol/L Ca^2+. To measure water hardness, a sample of groundwater is titrated with EDTA, a chelating agent, in the presence of the indicator eriochrome black T, symbolized here as In. Eriochrome black T, a weaker chelating agent than EDTA, is red in the presence of Ca^2+ and turns blue when Ca^2+ is removed. Ca(ln)^2++ EDTA rightarrow Ca(EDTA)^2++ In A 50.00-mL sample of groundwater is titrated with 0.0500 M EDTA. Assume that Ca^2+ accounts for all of the hardness in the groundwater. If 10.00 mL of EDTA is required to titrate the 50.00-mL sample, what is the hardness of the groundwater in molarity and in parts per million of CaC03 by mass?

Explanation / Answer

Hardness in groundwater is due to the presence of metal ions, primarily Mg^2+ an

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