Question

Hi guys why is magnesium ribbon cleaned before it's reaction with oxygen

Answer 1

When magnesium ribbon is stored, it's reacts with oxygen to get a layer of magnesium oxide on its surface. The layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen.
The magnesium ribbon is cleaned with sand paper for removing this layer so that the underlying metal can be exposed to air.

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Answer 2

♤ 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.