18. To determine the H2S and SO2 content in the air, it was passed through three absorbers connected in series. The first absorber contained an ammonia solution of Cd2+ to precipitate the sulfide as CdS, the second contained 10.0 ml of a 0.0396 N solution of I2 to oxidize SO2 to , and the third contained 2.0 ml of a 0.0345 N solution of thiosulfate to absorb I2 removed from the 2nd absorber. 25 liters of air were passed through the setup, and then a certain amount of pure nitrogen was passed to displace the last traces of SO2 from the 1st absorber into the 2nd. After acidification, 20.0 ml of a 0.0396 N solution of I2 were added to the solution from the 1st absorber, and 7.45 ml of the thiosulfate solution were used to titrate the excess. The solutions from the 2nd and 3rd absorbers were combined and the unreacted I2 was titrated with 2.44 ml of thiosulfate solution. Calculate the content (mg/l) of SO2 and the analyzed air.

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