Key concepts
Physical science
Chemical elements
Chemical reactions

What happens when you mix two common kitchen chemicals with a little food coloring, paintbrushes and friends? Find out with this bubbly sidewalk activity that acts like an art project but is really super scientific. It's is a great way to introduce kids to chemical reactions in physical science, yet keep the mess outside.

Acetic acid and sodium bicarbonate might sound super specialized, but they are the main compounds in two popular household products: vinegar and baking soda. Both are extremely dynamic substances; they are used medicinally, in edible recipes, and as cleaning agents. Put them together, and you've got yourself a bona fide chemical reaction on your hands.

When acetic acid is mixed with sodium bicarbonate, it creates a compound called carbonic acid, which can be found lots of places in nature, including blood and even the ocean. But because carbonic acid is an unstable compound, a quick and violent decomposition reaction occurs, resulting in two new compounds—water (H2O) and carbon dioxide (CO2). The bubbling you see and fizzing you hear when the two compounds come together then break apart are physical evidence of the decomposition reaction. Think of the classic baking soda–and-vinegar volcano science fair project!

•    ½ box of baking soda
•    ¼ cup of cornstarch
•    1 cup of hot water
•    Food coloring
•    Washable paint (optional)
•    Bowls (as many as the number of colors you want to make)
•    Note: This recipe is per color, so multiply quantities by the number of colors you will have
•    White distilled vinegar
•    Spray bottle
•    Paintbrushes
•    Driveway or sidewalk
•    Water hose or rain (for cleanup)

For each color:
•    Mix the baking soda and cornstarch together in a bowl.
•    Carefully pour the hot water into the dry mixture, stirring with increasing vigor as to dissolve any lumps. Congrats! You have just made your white paint base. (If your mixture has too much cornstarch, it might turn into a funky substance called Oobleck that's hard to stir. Not to fear—just add more water and mix away. You can learn more about this odd mixture in the Oobleck activity.)
•    Now, add drops of food coloring to the white paint base until it suits your preferred color intensity. Here, you can also add a generous squirt of store-bought washable paint but that is optional and only provides extra vibrancy.
•    Note: This activity can get a little messy, so be sure to wear clothes that are up to the task!

•    Grab your paintbrushes and have a blast painting your driveway or sidewalk, being careful and courteous of pedestrians and cars. Draw shapes, write words or, to really "drive it home," try making shapes and letters to match the elements on the periodic table.
•    Once you've painted your outdoor surface, allow drying time of about five or 10 minutes. The reaction will work better this way.
•    While you wait for the paint to dry, carefully fill the spray bottle with the white distilled vinegar.
•    As a final step, let your kids use the spray bottle to burst vinegar all over the art and wait for the oohs and ahhhs!
•    What happened when the vinegar came into contact with the baking soda-and-cornstarch art? Does it remind you of any other substances you know of?

Observations and results
Did you see the science happen? When the vinegar (acetic acid) and baking soda (sodium bicarbonate) in the paint solution is combined, they make carbonic acid. But this is a very unstable compound, so instead of making a nice calm solution, they react by bubbling and fizzing. This chemical reaction is called a decomposition reaction. Where have you seen this sort of reaction before? Can you guess what the white residue is called resulting from the experiment? Sodium acetate! The rest of the elements from the carbonic acid reaction pair off and make H2O (water) and CO2 (carbon dioxide), which makes the bubbles you see.

This activity puts some common elements, such as hydrogen, carbon, oxygen and sodium to work for some outside fun. How many everyday elements can you identify in your home? Why not use construction paper and tape to label them? Table salt is sodium, Na on the periodic table, and water from the sink is H2O—a combination of (two) hydrogen atoms with oxygen, elements that are individually gaseous at room temperature.

This project is nontoxic and water-soluble. You are free to use a water hose to wash the project away or, to err on the ecofriendly side, just wait for the next downpour to let nature do the dirty work.

More to explore
"Periodic Table of Elements" from Scientific American
"Strange but True: Elemental Quest for the Building Blocks of the Universe," from Scientific American
"Ocean Acidification from CO2 Is Happening Faster Than Thought" from Scientific American
Chemistry for Every Kid: 101 Easy Experiments That Really Work by Janice VanCleave
Amazing Kitchen Chemistry Projects You Can Build Yourself by Cynthia Light Brown and Blair Shedd

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