2. To determine the calcium content in water, an excess of HgNH3Y2- was added to a 25.0 ml sample. The EDTA anion was generated on a mercury cathode:

HgNH3Y2- NH4 ↔Hgzh 2NH3 HY3- (where Y4- is the EDTA ion).
Ca2 HY3-NH3↔CaY2- NH4 .

To reach the end point, a current of 20.1 mA was required for 2 min 56 sec. Calculate the content of CaCO3 (mg/l) in the analyzed water.

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