Question

Iron does not burn on heating but iron fillings burn vigorously when sprinkled on the flame of the burner. Why does this happen ? Give reasons.

Answer 1

The reason an iron bar won't generally burn is because the oxygen can't get inside the bulk of the bar.The surface layer actually does burn, but that forms a layer of iron oxide on the surface that keeps the oxygen from getting to the rest of the iron. If you grind up the iron into powder and disperse it in the air, then the oxygen in the air can get to every part of it, and it can burn pretty easily and very hot.