Why should a magnesium ribbon be cleaned before burning in air?
A magnesium ribbon should be cleaned before burning in air to remove the magnesium oxide layer formed on its surface. The context mentions that magnesium oxide is formed due to the reaction between magnesium and oxygen present in the air. This layer accumulates on the ribbon when it is stored in air.
By rubbing the ribbon with sandpaper, this oxide layer is removed. This exposes the pure magnesium metal underneath, allowing it to burn properly with a dazzling white flame during the activity.
Explanation
The textbook context from Activity 1.1 instructs students to clean the magnesium ribbon by rubbing it with sandpaper. The explanation for why this is necessary comes from the observation that magnesium oxide forms when magnesium reacts with oxygen in the air. Since the ribbon is stored in air, a layer of magnesium oxide naturally forms on its surface. This layer must be removed to expose fresh magnesium metal for proper burning. The context confirms that magnesium burns with a dazzling white flame and changes into white magnesium oxide powder.