why is it necessary to store alkali-metals under hydro carbons?
Alkali metals (e.g. sodium and potassium) react violently with water and decompose the water to give off hydrogen which may be ignited by the heat of reaction. Alkali metals can also ignite spontaneously in air, especially when the metal is in powdered form and/or the air is moist as here in Florida.
Some suggestions for safe use and storage of alkali metals are listed below: 1. Store alkali metals under mineral oil or kerosene. Avoid using oils containing sulfur since a hazardous reaction may occur. 2. Use only special dry powder Class D fire extinguisher on alkali metal fires. 3. Any waste alkali metals should be placed in a labeled, leak proof container, covered with mineral oil and properly disposed of through the Office of Environmental Health and Safety.