To do a science experiment with Pop Rocks and soda, pour Pop Rocks into a balloon, and place the mouth of the balloon over a bottle of soda. The Pop Rocks drop into the soda bottle from the balloon and cause a chemical reaction to occur.
Using a funnel, empty an entire package of Pop Rocks into a balloon. Tap the funnel to ensure all of the Pop Rocks get inside the balloon. Carefully fasten the mouth of the balloon to an opened bottle of soda. Do not let any of the Pop Rocks fall from the balloon into the soda bottle until the balloon's mouth is firmly attached to the bottle.
When the setup is complete, hold the balloon up, and let the Pop Rocks drop into the bottle of soda. Observe how the soda reacts with the candy and causes the balloon to inflate slightly.
The experiment works because both Pop Rocks and soda contain carbon dioxide. Each Pop Rock has a small portion of carbon dioxide gas inside it but not enough to cause the balloon to inflate. When the carbon dioxide gas from the Pop Rocks combines with the soda, it allows more carbon dioxide to escape from the high fructose corn syrup of the soda. The increased concentration of carbon dioxide gas from both of these sources causes the balloon to inflate.