DIY: Frozen Baking-Soda Rocks

When scientists examine rocks from our planet or from far beyond it they can use a variety of methods to help identify what they are. The identity and composition of the rock can tell scientists a lot about the environment where they were made. Some rocks can be identified by adding acid to them; if acid is added and the rock reacts it may be a kind of Carbonate rock, like limestone or dolostone, which means it contains the chemical compound CO3. You can create your own kinds of carbonate “rocks” at home using baking soda, or sodium bicarbonate (NaHCO3).

Activity Age: All ages
Required Activity Time: 5 minutes active, 1 hour inactive while it freezes
Activity Clean-Up Time: 5 minutes

~1/4 cup baking soda
~2 Tablespoons Water (enough to make the baking soda into a thick paste)
Ice cube tray or candy mold
~1/4 cup vinegar

1. Put your baking soda into a bowl
2. Add the water
3. Use a spoon to mix the baking soda and water into a thick paste, adding more water or baking soda until the mixture reaches the desired consistency
4. Spoon the mixture into your tray and shake it gently to remove any bubbles
5. Freeze for ~1 hour
6. Remove from the freezer onto a play surface or plate
7. Use an eyedropper, spoon, or straw (place the straw in the liquid and cover the top, when you release your finger the liquid will also be released) to drop vinegar on your rocks and watch the reactions

Show us your carbonate rocks! You can email your photos to

Baking Soda and Water paste
Baking Soda and Water Paste
Your Baking Soda Carbonate Rocks should react like with vinegar

Extra things to Try
-Set up an experiment adding different amounts of water to the baking soda before freezing; does it change the reactions?
-Place objects in your rocks and dissolve the carbonate away to find your treasures
-Add a drop of food coloring in your tray in the middle of spooning the mixture into the tray. As you add the vinegar the coloring will show itself. You can also color the vinegar for a color mixing activity.
-Work with your student to set up and solve a dinosaur bone mystery:

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