why should a magnesium ribbon be cleaned before burning in air

Dear Student,

Magnesium ribbon is cleaned with a sand paper before burning to remove the layer of magnesium oxide. Magnesium, as we know is a very reactive metal. It combines with the oxygen present in the atmosphere to form a layer of magnesium oxide (MgO). This layer interferes in the further reaction of metal. Thus, magnesium is rubbed with sand paper to remove this layer. 

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