Why should we rub a magnesium ribbon with sand paper before burning it.
Answers
Since Magnesium is an reactive metal in the reactivity series, when it is exposed to oxygen it will form metal oxides. For example, when oxygen is mixed with one of these metals for an extended period of time, you will see rust form and a brownish color coat over it as a tint. With Magnesium, what will happen if exposed to oxygen for too long is create a white coating on the outside of it which will impede and effect the burning process.
Thus, when sanded with sand paper, we are able to remove this extra layer that is impeding the burning, so that it can burn as if it weren't exposed to years of oxygen.
♤ When Magnesium ribbon is exposed in the atmosphere it form a layer of magnesium oxide on its surface.
♤ This layer of magnesium oxide is stable compound to prevent further reaction of magnesium with oxygen.
♤ Hence, it should be cleaned before burning in air to remove this layer so that the metal can be exposed to air properly.