Steel wool is made predominantly of iron and only a very small percentage of carbon. It is extremely thin with a great surface area, in fact if a difference of potential is applied (9V), it will be heated up, reaching a temperature of around 700°C. Therefore , the steel wool will burn with oxygen from the air producing iron oxide. That means the oxygen atoms are added to the iron atoms when the product iron oxide is formed, and this will cause an increase of mass. Remember mass in reactions is n

Steel Wool Burning