Science Experiments

An Invisible Fire Extinguisher

Sun, 13th Nov 2005

Part of the show Parasites, Hookworms and Allergies

What you Need

A large glass or jug

Bicarbonate of soda

Vinegar

A candle

What to do

Put 3-4 teaspoons of bicarbonate of soda in the glass

Add a cm or so of vinegar

Wait for the foam to die away.

Light the candle

Imagine the glass was full of a liquid, and gently poar the imaginary liquid onto the candle flame.

What may happen

You should find that the candle gets put out without you having to touch it.

Why does it happen?

To burn the candle takes in oxgen (O2) reacts it with the candle wax to produce carbon dioxide (CO2) and water (H2O).

A glass of CO2 A burning candle

Locked up in the Bicarbonate of soda is a gas called carbon dioxide (CO2) and When you add the vinegar this is released, filling up the glass with carbon dioxide.  This carbon dioxide is heavier than air so it stays in the glass, and if you tip up the glass it will pour out and fall down in a stream.

Pouring the CO2

 

As carbon dioxide tends to exclude the oxygen from the candle and is a waste product of its burning the candle flame can't burn any more and goes out.

Carbon dioxide fire extinguishes work on this principle - they contain compressed carbon dioxide and when you use one on a fire, they exclude the oxygen and make the burning less efficient and put it out.

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