Science project

Self-Inflating Balloons

Research Question:

What happens when you mix an acid and a base?


  • Water bottle
  • Vinegar
  • Small balloon
  • Funnel
  • Teaspoon of baking soda

Experimental Procedure:

  1. Put the water bottle where it will stand upright securely, or have a partner hold it. Fill it halfway with vinegar.
  2. Give the balloon a good stretching, like you would if you were about to blow it up.
  3. Use the funnel to put the baking soda inside the balloon. Gently shake the balloon until all the baking soda goes to the bottom.
  4. Making sure none of the baking soda gets into the water bottle, carefully stretch the opening of the balloon until it’s completely over the opening of the water bottle. If it’s not a tight fit, your balloon is probably too big and you should use a smaller one instead.
  5. Once the balloon is attached to the water bottle, lift the rest of the balloon so that the baking soda falls into the vinegar. You might have to give it a gentle shake to make sure it all goes in.
  6. Watch the balloon inflate! What’s happening here is the vinegar, an acid, is creating a chemical reaction with the baking soda, a base. When the two substances mix, you get carbonic acid, which is unstable and decomposes (falls apart) to become carbon dioxide (the gas that’s filling the balloon!) and water. Since the carbon dioxide is much less dense than the stuff you used to create it, it wants to expand, and the balloon is stretchy enough to allow it to do just that!

Terms/Concepts: fluids, density

References: Phineas and Ferb Science Lab, published by Scholastic, Inc., pp. 12-13 (2011).

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