The non-metal that catches fire

The idea

The non-metal phosphorus catches fire when exposed to atmospheric air.

Why under water?

Sodium is stored in kerosene. Another substance, phosphorus, is stored in water, which is odd, because water was bad news for sodium! Why?

Phosphorus is a non-metal. If it were left in the open air, what do you think would happen?

• Nothing at all
• It catches fire
• It turns into water

Phosphorus in air and in water

Tap each container to put a piece of phosphorus in. Compare the air with the water.

A substance kept under water

The non-metal phosphorus catches fire when it is exposed to atmospheric air. So phosphorus is stored in water.

Both sodium and phosphorus are stored so that the air cannot reach them: sodium in kerosene, phosphorus in water.

• Phosphorus is kept in | What happens
• Air | catches fire
• Water | safe: no air, no fire

Notes

Phosphorus, a non-metal, catches fire when exposed to atmospheric air, so it is stored in water.

Check yourself

What does phosphorus do when exposed to atmospheric air?

Where is phosphorus stored?

Phosphorus is stored in water because...

Which pair matches a substance with how it is stored?

• It catches fire — correct. Yes!
• It stays the same. It catches fire in air.
• It dissolves. It catches fire in air.
• In the open air. In air it catches fire.
• In water — correct. Yes! Water keeps the air away from it.
• In kerosene. Sodium is stored in kerosene. Phosphorus is stored in water.
• it is a metal. Phosphorus is a non-metal.
• it catches fire when exposed to air — correct. Yes! Water keeps air away.
• it reacts vigorously with water. Non-metals generally show no reaction with water.
• Sodium in kerosene, phosphorus in water — correct. Yes! Each is kept away from the air.
• Sodium in water, phosphorus in kerosene. Sodium reacts vigorously with water.
• Both in the open air. Both would react or catch fire in air.