Why are alkali metals stored under oil?

Alkali metals are stored under oil to prevent them from reacting with oxygen and moisture in the air.

Alkali metals, which include lithium, sodium, potassium, rubidium, caesium, and francium, are highly reactive due to their single electron in their outermost energy level. This makes them eager to participate in chemical reactions, particularly with oxygen and water vapour present in the atmosphere. If left exposed to air, alkali metals can react vigorously, often resulting in combustion or explosion. This is especially true for the heavier alkali metals like potassium, rubidium, and caesium.

To prevent these potentially dangerous reactions, alkali metals are stored under oil. The oil acts as a physical barrier, preventing the metals from coming into contact with the air. This is a simple and effective way to manage the reactivity of these metals and ensure they can be stored safely.

The type of oil used can vary, but it's typically a substance like mineral oil or paraffin oil. These oils are chosen because they do not react with the alkali metals and are not water-based, as alkali metals also react violently with water.

In a laboratory setting, it's crucial to handle alkali metals with care. Even when stored under oil, they should be handled with non-metallic tools to avoid sparks that could ignite a reaction. If an alkali metal does catch fire, it's important to remember not to use water to extinguish it, as this will only fuel the reaction. Instead, a Class D fire extinguisher, designed for metal fires, should be used.

In summary, the storage of alkali metals under oil is a crucial safety measure in both industrial and educational chemistry settings. It allows these highly reactive metals to be used safely in a wide range of experiments and processes.