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why are alkali metals stored in oil

Alkali metals are stored under oil because they are extremely reactive and would otherwise react violently with air and moisture, forming oxides or hydroxides and sometimes catching fire or even exploding.

Quick Scoop

Alkali metals like lithium, sodium, and potassium have a single electron in their outer shell, which makes them highly eager to react. If you leave a small piece of sodium in the open, it quickly reacts with oxygen and water vapour in the air, forming white crusts of oxides/hydroxides and releasing heat. In some cases, this heat is enough to ignite the metal, causing a fire. Storing these metals under oil (paraffin or kerosene) keeps air and water away from their surface, so they stay shiny, intact, and safe.

What “stored in oil” really means

  • The metal is completely submerged in a non‑reactive oil such as paraffin or kerosene.
  • The oil acts as a physical barrier, blocking oxygen and moisture in the air from reaching the metal.
  • The oil itself is largely unreactive toward alkali metals under normal storage conditions.

Mini sections

1. Why are alkali metals so reactive?

  • They have one valence electron, which they lose easily to form M+M^+M+ ions.
  • As you go down the group (Li → Na → K → Rb → Cs), this outer electron is further from the nucleus, so it is lost more easily and reactivity increases.
  • This high reactivity means even contact with humid air is enough to start a reaction.

Example: A fresh piece of sodium, when cut, looks shiny but quickly turns dull as it reacts with oxygen and water vapour to form sodium oxide and hydroxide.

2. What happens if they are not stored under oil?

  • They react with oxygen to form metal oxides, coating and degrading the metal.
  • They react with moisture or liquid water to produce metal hydroxides and hydrogen gas; the reaction releases heat and can ignite the hydrogen or the metal itself.
  • Larger pieces or more reactive metals (like potassium, rubidium, caesium) can produce flames or small explosions in contact with water.

3. Why specifically oil (kerosene/paraffin)?

  • Kerosene/paraffin is non‑aqueous (contains essentially no water), so it prevents contact with moisture.
  • It does not react significantly with alkali metals in normal conditions, so it is a safe “blanket” medium.
  • It has relatively low volatility, meaning it does not evaporate quickly and provides long‑term protection.

4. Lab safety angle (modern context)

  • Even under oil, alkali metals should be handled in small pieces, with forceps or non‑sparking tools, and kept away from water and acids.
  • If a fire occurs, water must not be used; special Class D (metal fire) extinguishers or dry sand are recommended.
  • This practice remains standard in school and university labs in 2026 whenever sodium or potassium demonstrations are done.

Short numbered recap

  1. Alkali metals are highly reactive with oxygen and water.
  2. Exposure to air leads to rapid formation of oxides and hydroxides, plus heat release.
  1. In some cases, this reaction can ignite the metal or hydrogen gas, causing fire/explosion.
  1. Storing them under non‑reactive oil (kerosene/paraffin) keeps air and moisture away.
  1. This preserves the metal and greatly improves safety during storage and handling.

Information gathered from public forums or data available on the internet and portrayed here.