Why magnesium ribbon is cleaned before burning in air

Magnesium ribbon is cleaned before burning in air for the following reasons:

1. Removal of Oxide Layer: Magnesium metal forms a protective layer when exposed to air. This layer is primarily of magnesium oxide, which prevents further oxidation of magnesium. Before burning, the ribbon is cleaned to remove this layer so that the metal can directly react with oxygen.

2. Ensuring Proper Reaction: The presence of the oxide layer might hinder the burning process as it is less reactive than magnesium itself. Cleaning the ribbon ensures that the reaction between magnesium and oxygen is smooth and complete.

3. Accurate Observations: For experimental purposes, it's important to have accurate observations. The presence of the oxide layer might influence the observations and results of the experiment. Therefore, to avoid any discrepancies in the observations, the magnesium ribbon is cleaned before burning.

4. Safety Measures: Magnesium burns with a dazzling white flame. If the ribbon is not cleaned properly and there are patches of magnesium oxide, it may cause spluttering during the burning. This could be a potential safety hazard.

In conclusion, cleaning the magnesium ribbon before burning is crucial for the reasons of safety, ensuring a proper reaction, and obtaining accurate experimental results.