Hardness in groundwater is due to the presence of metal ions, primarily mg2+ and ca2+ . hardness is generally reported as ppm caco3 . 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 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. red blue ca(in)2+ + edta ⟶ ca(edta)2+ + in a 50.00 ml sample of groundwater is titrated with 0.0450 m edta . if 13.70 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? assume that ca2+ accounts for all of the hardness in the groundwater.