Hardness in groundwater is due to the presence of metal ions, primarily mg2 and ca2 . hardness is generally reported as ppm caco3 or mmol/l ca2 . 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. redblue ca(in)2+ + edta --> ca(edta)^2+ + in a 50.00-ml sample of groundwater is titrated with 0.0600 m edta. assume that ca2 accounts for all of the hardness in the groundwater. if 12.00 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 caco3 by mass?