We go through so much baking soda and vinegar in my house that I have to buy it in bulk. (What can I say, I’m raising a couple of science geeks!). While they may never get tired of making those fizzy “explosions,” it’s getting a little overdone for me.  This ‘cool’ activity results from a similar chemical reaction, but produces a chilly foam that kids of every age will love to stir and squish!

LEARN SCIENCE VOCABULARY:

Chemical reaction – When two things come together and change into something else, this is a chemical reaction.  In this case, it is citric acid and baking soda (a.k.a. sodium bicarbonate) meeting up to produce carbon dioxide gas that make the bubbles in our foam. Things that have gone through a chemical reaction are permanently changed!

Endothermic – A reaction that absorbs heat, causing the product to feel cool.  The opposite of this is an exothermic reaction, which releases heat and causes the product to feel warm.

MATERIALS NEEDED: 

• Baking soda
• Citric acid (You can find this near the canning items at Walmart or some grocery stores. It’s used as a preservative when canning tomatoes.)
• Clear hand soap
• Water
• Food coloring
• Small plastic containers (Greek yogurt cups are the perfect size!)
• Spoons for stirring

HOW TO MAKE IT:

1. Mix 2 squirts of clear hand soap with about 1/2 cup of water in the plastic containers.  Add a few drops of food coloring to each one and mix in.

   

2. If you haven’t already, TAKE EVERYTHING OUTSIDE (or put a giant tarp down…things got real messy for us from this point on!).
3. Add about 1 tablespoon of baking soda to each container.  (I had my kids stirring the colored mixtures while I did this.  You don’t really need to mix it continuously, but it made them feel like they were actively participating and I could maintain control of the scooping part!)
4. Now add about 1 tablespoon of citric acid and mix in to start the CHEMICAL REACTION.  Foam will begin to form and spill over the sides of the container!  Kids can stick their hands in and feel that the foam is cool to the touch. (Citric acid is a food-grade mild acid, similar to the acidity of a lemon, so you don’t have to worry about little kids getting it all over themselves or even in their mouths.)

   

5. After the reaction has slowed, you can continue to add baking soda and citric acid to the liquid remaining in the container and keep the CHEMICAL REACTION going to create more foam. Or try pouring the containers together to see what happens when the colors are mixed! (For another ‘cool’ color-mixing activity, try Color Mixing with Ice.)

   

*EXTENSIONS FOR OLDER KIDS – There are several different ways to change this experiment to see how each variable (ingredient) affects the outcome!

• Try the experiment without the soap.  How does this change the bubbles?
• Combine dry citric acid and baking soda to see if a reaction occurs.  (It will not. Water is needed as a CATALYST – the thing that jump starts the reaction.)
• Try varying the proportions of citric acid and baking soda…for example, 1 Tbsp of citric acid to 2 Tbsp of baking soda, and vice versa.  What effect does that have on the size of bubbles or rate of reaction (how quickly the foam begins to form)?

  

THE SCIENCE BEHIND IT:

When dissolved in water, citric acid and baking soda react in a manner similar to that of baking soda and vinegar, the ingredients for the common ‘erupting volcano’ activity.  (Try Baggie Bombs if you want to a fun way to check out how vinegar reacts with baking soda!)  This CHEMICAL REACTION produces carbon dioxide gas (which form the bubbles) and water.  The addition of dish soap is what causes the foam by trapping the tiny carbon dioxide bubbles before they can pop. The reaction is also taking in heat (ENDOTHERMIC), which causes the foam to feel cool to the touch.  A lot of fizzy bath bombs contain a combination of citric acid and baking soda – the bubbly reaction begins when you drop it into the bathwater!