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Firefighting CO2 Balloons

In this demonstration, students witness carbon dioxide being produced by a reaction between two common household chemicals. They then use one of the physical properties of carbon dioxide to extinguish a flame with what looks like magic.

Mixing vinegar (acid) and baking soda (base) creates a chemical reaction. When the two combine they create carbon dioxide (CO2) gas. When baking soda is mixed with an acid such as chocolate, yogurt, buttermilk or honey in muffins or a cake, the same type of chemical reaction occurs. The released bubbles of CO2 fluff up the batter.

When the reaction takes place inside a closed balloon, the CO2 pushes against the walls of the balloon, causing it to expand. This serves as evidence that a gas is being produced inside the balloon.

CO2 is heavier than air. When released from the balloon into a glass, it will collect at the bottom. If this CO2 is "poured" over the flame, it pushes the lighter air out of the way. The flame needs the oxygen in the air to burn, so the carbon dioxide puts out the flame.

One type of fire extinguisher uses carbon dioxide. It pushes oxygen out of the way, putting out the fire. This type of extinguisher leaves no mess behind, as opposed to chemical-, water-, and foam-based extinguishers. Carbon dioxide extinguishers are used in theatres, computer rooms, or other sensitive telecommunication areas.

If you wait too long to "pour" the carbon dioxide gas on the flame, the demonstration will not work. One of the properties of gas is that it will diffuse evenly in the space that surrounds it. This is why we do not live in a layer of CO2 where the life expectancy would be 2.5 minutes!

Because CO2 is colourless, you cannot see it being poured. However, it is possible to see how CO2 sinks and can be poured when working with dry ice (frozen CO2) because the cold COcauses water in the air to form mist. Hence working with dry ice could be a nice follow-up to this activity.


  • Describe the effects of an acid/carbonate-base reaction.

  • Compare the relative weights of two gases.

  • Describe the properties of gases.

  • Describe the elements required for a flame to burn.


  • Part 1: Producing the CO2
    1 teaspoon (5 ml) baking soda
    ¼ cup (60 ml) vinegar
    1 litre plastic pop bottle or conical (Erlenmeyer) flask
    1 balloon

  • Part 2: Extinguishing the CO2
    CO2-filled balloon-bottle contraption from Part 1
    1 balloon
    2 tall glasses
    candle with candle holder
    matches or lighter

Key Questions

  • The balloon expands when CO2 is added to it. Why doesn’t the bottle expand like the balloon?
  • If CO2 is heavier than air, predict what will happen if the CO2 trapped in the balloon is poured onto the air in the glass?
  • Some fire extinguishers use CO2 to put out fires. Why are these more effective than just blowing air onto on a fire?

What To Do

Part 1: Producing the carbon dioxide gas

  1. Place the plastic pop bottle/conical flask on the table.
  2. Carefully pour the vinegar into the bottle.
  3. Open up the mouth of the balloon (put the first two fingers or thumbs on each hand inside the mouth of the balloon and stretch).
  4. Ask a student to spoon the baking soda into the balloon.
  5. Without spilling any of the baking soda, stretch the mouth of the balloon over the neck of the bottle.
  6. Turn the balloon upright so that the baking soda inside the balloon pours into the bottle with the vinegar.
  7. Swirl the bottle a little to mix the contents.
  8. The mixture will fizz and produce bubbles, filling the balloon with carbon dioxide.
  9. Do not dismantle the balloon and bottle.

Part 2: Extinguishing a flame with carbon dioxide gas

  1. Light the candle.
  2. Ask a student to blow up the second balloon, trapping the air by pinching the neck of the balloon. Do not tie the balloon
  3. Ask the student to empty the air-filled balloon contents into one of the glasses by opening the balloon above it.
  4. Ask the student to pour the air from the glass onto the candle. Nothing should happen.
  5. Remove the CO2-filled balloon from its bottle, keeping the CO2 trapped by pinching the neck of the balloon. Do not tie the balloon.
  6. Carefully empty the contents of the CO2 balloon into the second glass.Pour the CO2 onto the candle. The flame should go out!


  • What could you use instead of vinegar to create a similar reaction? Test your hypothesis.
  • Is a balloon blown up by a person heavier or lighter than a balloon blown up by a balloon pump? Test it, and compare both these balloons to a balloon blown up using the baking soda vinegar reaction.