Question

Why should a magnesium ribbon be cleaned before burning in air? ​

Answer 1

Answer:

Magnesium being a passively but still moderately reactive metal reacts slowly with the oxygen available in the air to form a layer of Magnesium oxide on its surface due to which this Magnesium pxide layer can cause hinderance to burning of ribbon when made to react with oxygen in high temperature apparutus.

So, to avoid any hinderance and to make the oxygen directly react to magnesium ribbon it's first cleaned before burning in air to remvoe the Magnesium oxide layer formed.

Answer 2

magnesium ribbon reacts with carbon dioxide present in the air to form a protective and inert layer of magnesium carbonate. This layer is unreactive and hence, needs to be cleaned with sand paper before burning in air.