When you burn steel wool it actually gets heavier I will burn some steel wool and see what happens to the mass as the steel wool burns. Steel wool is made mostly of the element iron (Fe). When the steel wool is heated the thin strands have a large amount of surface area which allows the iron in the steel wool to burn and combine with the oxygen in the air. This accelerated oxidation is rusting. The steel wool weighs more after it is burned. When iron burn iit forms the compound iron oxide Fe2O3.

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