You have a plume of hexavalent chromium as chromate (CrO4 2- ) that will be reduced to insoluble Cr3 . The molecular mass of chromate is 115.9 g/mol. The concentration is 238 ppm in water. How much zero valent iron (ZVI) will you need to add to completely transform the chromium. The ZVI will be converted to Fe2 . The molar mass of iron is 55.9 g/mol.