Things you need:

• Large glass container-like 10 gallon fish tank
• 1 cup of vinegar
• ½ cup of baking soda
• Bubble solution and wand

The Experiment:

As always, please do any science experiments under the supervision of an adult. First, spread the ½ cup of baking soda onto the bottom of the fish tank. Then pour in one cup of vinegar. The mixture will fizz and bubble as they react to form carbon dioxide gas and water as the final product. When the fizzing is done, blow some bubbles so that they land in the tank, without blowing directly into the tank. This may take some practice. If you blow directly into the tank, you will blow carbon dioxide gas out of the tank. As the bubble floats down into the tank, it will stop and sit on the layer of carbon dioxide gas. Observe what happens to the bubbles.

• What you could also try with an adult is to light a match and slowly lower it into the tank. What happens?
• Because the tank contains only carbon dioxide, please keep a good distance from the bottom of the tank.

So that’s how it works…

Because carbon dioxide gas is heavier than air, it will collect in the tank and stay there, similar to a liquid. The bubbles float on the top of the carbon dioxide layer because the air inside them is lighter than the carbon dioxide. The bubbles will slowly sink to the bottom of the tank and grow larger as they sink. When the bubble is on the carbon dioxide layer, the carbon dioxide will begin passing through the thin soapy skin of the bubble and begin to fill the bubble with the heavier gas, causing the bubble to sink to the bottom of the tank. The carbon dioxide moves in faster than the air moves out, so the bubbles also grow bigger.

With the match, the flame should be put out, once the match reaches the carbon dioxide. For fire to occur, you need three things: 1) Fuel (matchstick); 2) Oxygen; and 3) Heat source (flame). Because the carbon dioxide is heavier then the air, it displaces all the air, including oxygen, from the bottom of the tank. When the match is placed into the carbon dioxide, it no longer has any oxygen to burn, so the flame goes out. You could also try scooping some carbon dioxide (you’ll have to use your imagination) out of the tank with a cup and pouring it onto a candle to see if you can put the flame out.

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