Oxygen Feeds the Flame

Why it matters

Drop a strip of shiny magnesium ribbon into a jar of pure oxygen and touch it with a flame. It bursts into a blinding, dazzling white light — far brighter than it ever burns in ordinary air!

Predict first

A glowing wooden splint (no flame, just a red glow) is pushed into a jar full of oxygen. What happens?

Oxygen supports burning. A glowing splint relights and flares up in oxygen — this is the standard test used to show that a gas is oxygen.

• It goes out at once, because a jar traps the splint
• It bursts back into a bright flame — correct
• Nothing changes; it keeps glowing the same
• It turns to ice because gases are cold

What you do

Run the reaction on the bench: light the magnesium ribbon and let it burn in oxygen. Watch the dazzling white light and the fine white ash it leaves behind. That white powder is magnesium oxide. Notice how the metal combines with oxygen from the air as it burns.

Check yourself

When magnesium burns in oxygen, what white solid is formed?

Magnesium joins with oxygen from the air to form a new substance, magnesium oxide, seen as a fine white ash.

How can you test an unknown gas to show it is oxygen?

Oxygen supports combustion, so it relights a glowing splint. That flare-up is the classic oxygen test.

A lighted candle is covered with an upturned glass jar. After a while the flame goes out. Why?

Burning needs oxygen. Once the trapped oxygen in the jar is used up, the flame cannot continue and it goes out.

• Magnesium oxide — correct
• Magnesium ice
• Pure oxygen gas
• Water only
• Bubble it through lime water and watch it turn milky
• Put a glowing splint into it and see it relight — correct
• Smell it for a sharp smell
• Shake it and listen for a pop
• The candle used up the oxygen inside the jar — correct
• The glass jar is too cold for fire
• Candles can only burn outdoors
• The wax turned into water