138. Задачка по химии №013 853

81. A portion of the siderite mineral equal to 0.9938 g is dissolved and brought in a volumetric flask to a volume of 20 cm3. For the titration of iron ions, previously reduced to Fe2 for 50.00 cm3 of this solution, 20.50 cm3 of a KMnO4 solution with T KMnO4 / Fe = 0.005861 g / cm3 is spent. Determine the mass fraction of iron.