Summary: Candles are placed on "stairs". Carbon dioxide is poured over the candles. The candles extinguish.

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Estimated Time: 5 - 10 minutes

Materials Needed:

• stair step set up (see picture)
• several tea candles
• matches
• pitcher with lid
• 1 box baking soda
• 1 bottle of vinegar

Safety Notes: Use proper fire safety with candles. Follow the safety procedures mentioned in previous activity for the acid/base column.

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Introduction: In the last activity, we could see where the carbon dioxide moved by looking at the water vapor "smoke" created. We will use this to help us learn more about carbon dioxide.

Procedure:

• Place stair step apparatus on table. Place candles inside and light them.
• Have an adult or student mix baking soda and vinegar in the pitcher and close the pitcher. Complete this out of sight of the class.
• Remember gases act like liquids so they can be poured. Pour the gas in the pitcher over the candles. You will not see the gas. Do not pour the liquid out.
  • What is happening to the candles now?
  • Why do you think this is happening?
  • What do you think was in the pitcher?
  • What does this tell us carbon dioxide might be good for?

Think About It:

All Levels:

We poured a gas from the pitcher that you could not see. What do you think it was? It was carbon dioxide. We made it using vinegar and baking soda, just like in our first experiments. We caught it in the pitcher by putting the lid on.

Why did the carbon dioxide flow down? Why didn't it float up? We learned in our last experiment that carbon dioxide is more dense than air. That is why it went down when we poured it.

Why do you think the candles went out? Candles need oxygen to burn. The carbon dioxide blocked any oxygen from getting to the candles, causing them to extinguish. [High School Note: In fact carbon dioxide is produced when you burn things. Since we put more of the product around the reaction, the reaction is does not go forward.]

Because carbon dioxide works this way, what might it be good for? Can you think of anything used in a lab or in a house that might use carbon dioxide? Carbon dioxide is sometimes used in fire extinguishers.

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Teaching Tips:

• We strongly suggest this activity be completed as a class demonstration.
• The amount of baking soda and vinegar needed depends on the pitcher used. Experiment beforehand to find a good approximation. Do not create too much carbon dioxide or the lid may pop off of the pitcher or liquid may spew out of it from pressure.
• The experiment works best when done away from air vents or fans. The air needs to be still so that the flow of the carbon dioxide is not disrupted.
• This activity is recommended as a demonstration.
• You may complete the activity with candles inside of a jar or a beaker. If you do not have a stair step, you can create a ramp and trough from cardboard and aluminum foil.