Why are alkali metals stored under oil?

Alkali metals are stored under oil to prevent their reaction 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 the outermost shell. 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.

To prevent such hazardous reactions, alkali metals are stored under oil. The oil provides a physical barrier between the metal and the air, effectively cutting off the supply of oxygen and moisture. This is a simple yet effective method to prevent unwanted and potentially dangerous reactions.

The type of oil used can vary, but it is typically a hydrocarbon like paraffin oil. It's important to note that the oil itself does not react with the alkali metals. It merely acts as a protective layer, preventing the metals from coming into contact with reactive substances in the air.

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 the metal. If an alkali metal does catch fire, it's important not to use water to extinguish it, as water can react violently with alkali metals. Instead, a Class D fire extinguisher, designed for metal fires, should be used.

In summary, the storage of alkali metals under oil is a necessary safety measure due to their high reactivity. It prevents contact with oxygen and moisture, thus avoiding violent chemical reactions.