Question

Why should a magnesium ribbon be cleaned before it is burnt in air?

Answer 1

$\huge{\mathfrak{\underline{Answer:}}}$

When stored it reacts with oxygen to form a layer of magnesium oxide on its surface. This layer of magnesium oxide being a stable compound prevents further reaction of magnesium with oxygen. The magnesium is cleaned before burning in air to remove this layer so that the metal can be exposed to air properly

Answer 2

The surface of magnesium ribbon will mostly be magnesium oxide which forms a thin, tightly bound layer on the surface of the metal. This impedes further reaction drastically but does not stop it altogether. hence, to proceed the experiment we need to clean the magnesium ribbon with a sandpaper to remove the magnesium oxide layer.