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STEM Activities

STEM Activity: Balloon Head

In this experiment, participants will blow up a balloon using carbon dioxide (CO2) gas produced by a baking soda and vinegar reaction. They will predict how much baking soda is needed to blow up their “balloon head” to be the right size for a hat to fit.

Materials Needed

  • Aluminum roasting pan
  • Baking soda
  • Balloons
  • Funnel
  • Hats
  • Permanent marker
  • Spoon
  • Vinegar
  • Water bottles


  1. Collect or purchase one empty bottle (such as a 12- or 20-ounce soda pop bottle or water bottle), a bottle of vinegar and two hats (e.g. a paper hat or ball cap).
  2. Divide your work surface into three activity sections and place the supplies as follows:
    1. Section One: Place the balloons, permanent marker and hats in this area. Here, participants will collect their balloon and draw a customized face on it.
    2. Section Two: In this area, collect the following items: an aluminum roasting pan filled with baking soda, a funnel, a spoon and a water bottle filled with about one-half cup of vinegar. This is the area where participants will collect the items needed for the experiment.
    3. Section Three: Create an open space for experimentation.
      1. Make a sample balloon head on a bottle by completing the experiment described below, for participants to see.
      2. Pour one-quarter cup of baking soda into a clear cup for participants to see how much was used.
      3. Practice demonstrating how to stretch the balloon over the opening of the bottle.

At-Home Instructions

  1. Explain to participants that they will be mixing baking soda and vinegar to cause a chemical reaction that will produce CO2 gas and blow up the balloon. The CO2 will create a balloon head that will fit into a hat of their choice.
  2. Have participants select a hat they want to fit on their balloon once it is blown up with CO2 from the reaction. Show participants the sample balloon head and how much baking soda was used.
  3. Encourage participants to make a prediction as to how much baking soda they will need to react with the vinegar in order for the CO2 to fill the balloon, making it just the right size to fit the hat they have selected.
  4. Give participants a marker and instruct them to create a face on their balloon.
  5. Give participants a funnel and spoon to pour baking soda into their balloon. Remind them to put in the amount that they think will make their hat fit just right.
  6. Explain to participants that once they have their baking soda in the balloon, they should stretch the opening of the balloon over the top of one of the water bottles filled with vinegar, allowing the balloon to rest on the side of the bottle. It’s important that the baking soda does not fall into the vinegar prematurely.
  7. Have participants count down from five to one, and then lift their balloon straight up and down, dumping the baking soda into the vinegar to cause the reaction that will blow the balloon up with CO2 while it sits on the bottle.
  8. Encourage participants to try the hat they selected on their balloon to see if it fits.
  9. Assist participants in tying their balloon closed.

What Are We Learning?

When mixing baking soda and vinegar, there appears to be just one reaction, but there are actually two! One reaction is happening quickly after the other. Vinegar is an acid (acetic acid) and baking soda (sodium bicarbonate) is a base. When they mix, an acid-base reaction occurs and produces carbonic acid. The carbonic acid immediately separates into CO2 and water. The bubbles produced by the reaction are from the CO2 gas escaping the solution that is left. CO2 is heavier than air, so it flows almost like lava or water when it bubbles out of a container like a water bottle. What is left in the bottle is a dilute solution of sodium acetate in water. Once the CO2 is released, the solution will not react again if more vinegar or more baking soda is added.

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