Question

Magnesium ribbon is rubbed with sand paper before burning it. The reason of rubbing the ribbon is to:

• A. Remove moisture condensed over the surface of the ribbon.
• B. Generate heat due to an exothermic reaction.
• C. Remove magnesium oxide formed over the surface of magnesium.
• D. Mix silicon with magnesium with sandpaper (silicon dioxide) for lowering ignition temperature of the ribbon.

Answer 1

The correct option is C Remove magnesium oxide formed over the surface of magnesium.

When exposed to air many metals will slowly react with oxygen in the atmosphere to form metal oxides and magnesium is one of those metals. You are probably familiar with rust which is simply the oxide that forms when iron is exposed to oxygen in the air. With magnesium, the oxide layer forms a white coating on the outside of the metal that will slow down or interfere with the burning process. The ribbons should be sanded with a fine sandpaper, therefore, to remove the oxide layer and thereby helping in the desired or complete burning of magnesium. Burning magnesium results in magnesium oxide and also some magnesium nitride (reaction with nitrogen in the air). Burning speeds up the conversion of magnesium to magnesium oxide in air.