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 CaCOj 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 Ca2* and turns blue when Ca2* is removed. Ca(ln)^2+ + EDTA rightarrow Ca(EDTA)^2 + + In A 50.00-mL sample of groundwater is titrated with 0.0800 M EDTA. Assume that Ca2+ accounts for all of the hardness in the groundwater. If 13.50 ml of EDTA is required to titrate the 50.00-mL sample, what is the hardness of the groundwater in molarity edit per million of CaCOj by mass?

Explanation / Answer

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

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