7. 1.00 g of cobalt was placed in a solution containing nitrates of two metals. After the end of the reaction, the precipitate was filtered, its mass was 3.52 g. 1.00 g of cobalt was added to the obtained filtrate, after the end of the reaction the precipitate was filtered off, its mass was 3.02 g. 1.00 g of cobalt was added to the obtained filtrate again, after the end of the reaction the precipitate was filtered, its mass was 2.01 g. 1.00 g of cobalt was added to the filtrate again, after the end of the reaction the precipitate was filtered off, its mass was 1.51 g, but the filtrate contained only cobalt nitrate. Determine what salts the solution contained and what was their mass! (1/54)8. When 1.6 g of black powder was treated with a preponderance of concentrated sulfuric acid, only 0.02 mol of metal(II) sulfate, 3.2 g of SO2, and 1.08 g of water were obtained. Determine the formula of the black powder!