How to make inflatable conversation hearts

Watch to learn how to do some Valentine’s themed science fun!


  • An empty bottle
  • 4 Alka Seltzer tablets 
  • 1/2 cup water for each round
  • A balloon
  • A Sharpie


  1. Break the Alka Seltzer tablets into small pieces and drop them into the bottom of the bottle.
  1. Brainstorm a couple of your favorite conversation heart messages and use the Sharpie to draw them on the balloons. (optional)
    *TIP:  the conversation heart is more crisp and clear if you first blow it up with air, temporarily pinch it closed with my fingers and then draw the picture. When drawing the conversation heart while flat and empty, the image stretches too much when the balloon is inflated.
  1. After making a prediction about what will happen, carefully pour the water into the bottle.
  1. Then, speedily stretch the mouth of the balloon with your fingers and stretch it over the rim of the bottle and watch the balloon inflate!

*Science behind it: Similar to the reaction that occurs when you mix baking soda and vinegar, when you pour water on Alka Seltzer tablets, carbon dioxide gas bubbles begin forming.  These gas bubbles rise up in the bottle, filling the balloon with carbon dioxide gas.*

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