Some bath products fizz and make bubbles when added to water. Ever wonder why? Discover how fizzy bath bombs can not only invigorate your bathtime but your science lessons, as well! With this easy spa science project, you’ll first make your own fizzy bath bombs, then experiment with them to discover acid-base chemical reactions. (Adult supervision recommended.)

What You Need:fizzy bath bombs - download PDF

  • 1/2 cup baking soda
  • 1/4 cup citric acid in powder form
  • 1/4 cup cornstarch
  • 2-1/5 tablespoons Epsom salts
  • 1-1/4 tablespoons olive or almond oil
  • 1-3/4 teaspoons water
  • 1/4 teaspoon fragrance oils
  • 1/8 teaspoon borax
  • Plastic mixing bowl
  • Gloves
  • Jar with lid or other airtight container
  • Molds* or ice cube trays

What You Do:

  1. Put the gloves on and combine the baking soda, citric acid, corn starch, and Epsom salts together in a bowl. Mix well and set aside.mix fizzy bath bombs
  2. Combine the oils, water, and borax in a jar. Cover it with the lid and shake vigorously to mix the ingredients well.
  3. Slowly add the liquid mixture to the dry mixture, a few drops at at time, stirring continuously and quickly to minimize fizzing. When fully mixed, the mixture will be very dry and crumbly.
  4. Pack the mixture into molds or ice cube trays and let rest for two days. *We used the Bath Bomb Science Kit, which contains the non-household ingredientsyou need—including the molds shown here—in the amounts you need.
  5. After two days, carefully remove the mixture from the molds. 
  6. Take one of the finished bath bombs and drop it in water. What happens?

What Happened:

Bath fizzies, fizzy bath bombs, effervescent bath bombs—no matter what you call them, fizzy bath bombs are a bath time treat that shows how acids and bases react when mixed together. In this fizzy bath bomb science project, the baking soda is the base and the citric acid is, well, the acid. But the chemical reaction of this acid-base combination can be controlled by the other ingredients in the bath bomb.

The cornstarch and Epsom salts in the bath bombs both act as liquid absorbers to help keep the baking soda and citric acid from reacting with each other when liquids are added. They are also helpful if you live somewhere with high humidity. The borax acts as both a preservative and an emulsifier, stabilizing the acid and the base within the bath fizzies. It helps prevent them from reacting with each other before entering the water. If that effervescent reaction happened before they hit the bath, yo’d have quite a mess!

Water is the catalyst that causes the reaction to occur. It dissolves the solids and allows the ions in the acid and the base to move and collide with each other, causing a chemical reaction. A catalyst is something added to a chemical mixture that speeds up the chemical reaction time. This reaction forms carbon dioxide, a gas, which rises to the surface of the bathwater in the form of bubbles. The oils and the fragrances are useful as a liquid to help form the fizzy bath bombs as well as leave the skin smooth and scented.

To make this spa science project even simpler, download a free fizzy bath bomb printable here. And check out the complete fizzy bath bomb science kit.

For further study, try these other fun spa science projects: