56. Solving a chemistry problem

73. In a coulometric cell containing 25.0 cm3 of a 0.200 mol/dm3 solution of KI, I2 was generated for 4 min at a current strength of 10.0 mA (η = 100%). Then 2 dm3 of a gas containing H2S was passed through the solution. Unreacted iodine was reduced with 10.0 cm3 of a 0.0010 mol/dm3 solution of Na2S2O3, and the excess of the latter was titrated with iodine, spending 2 minutes for titration. 45 s at 3.0 mA. Calculate the content (mg/m3) of H2S in the gas (n.c.).