I burned copper (wool) [ 49.34 g] for a certain amount of time, and its color changed; (copper oxide formed)but the mass is still 49.34 g!! Why?
In all liklihood you did NOT burn the copper, you only burned the surface of the copper. In this case, the copper itself probably weighed a good deal more than the amount converted to oxide, so the mass change was unnoticeable. To really see the difference, you would need temps in excess of 3000 degrees and an oxygen-rich environment or some other method for fully oxidizing the copper. same is true for the steel wool except that steel will tend to flake away as it oxidizes (rather than forming a protective coat). Fully convert the steel wool and you will similarly see the mass change as oxygen is absorbed.
CuO is not copper burnt with oxygen. It's a chemical reaction in which pure copper is oxidized: 2Cu + O2 --> 2CuO Assuming 1 gram of copper is allowed to oxidize... more than 1 gram of CuO will be produced if you do the stoichiometry calculations.
