A magnesium ribbon should be cleaned before burning in air because it forms a layer of magnesium oxide (MgO) on its surface when exposed to air. This oxide layer is stable and does not burn easily, which slows down or prevents the pure magnesium underneath from burning effectively. Cleaning the ribbon with sandpaper removes this oxide layer and any other impurities, allowing the pure magnesium to burn with a bright, intense flame when ignited in air.
Why Cleaning is Necessary
- Magnesium is highly reactive and quickly oxidizes in air, forming a white magnesium oxide coating.
- This oxide layer acts as a barrier that inhibits further reaction with oxygen during burning.
- Removing this barrier ensures the ribbon burns properly, demonstrating the typical bright white flame of magnesium combustion.
Effect of Cleaning
- Sandpaper or abrasive cleaning removes the oxide layer.
- The clean, pure magnesium surface then reacts readily with oxygen on ignition.
- This results in efficient and complete combustion of magnesium to form magnesium oxide.
Thus, cleaning the magnesium ribbon ensures the reaction proceeds unimpeded, showing the characteristic bright flame and heat release of burning magnesium.
