Key concepts
Chemical reactions
Have you ever opened a fresh bottle of carbonated water or soda, poured a glass of it, and just watched as the bubbles fizzed upward in the glass? Have you ever wondered what those bubbles are? They're made of carbon dioxide gas, which was packed tight in the soda before you opened the bottle. Not only can that carbon dioxide gas give you a fizzy drink to enjoy, but it can also give you a show. How? By making candy conversation hearts "dance"! Along the way you will discover some of the fun chemistry for this entertaining activity. So this Valentine's Day if you receive some conversation hearts, you can grab a glass of soda and try out this science activity to explore another way to enjoy the candies—by watching them slowly dance!
A carbonated beverage, such as a bottle of soda, is packed full of dissolved carbon dioxide gas. But you don't see bubbles of carbon dioxide gas while the bottle is still sealed. Why is this? Soda in bottles (and cans) is prepared and kept in pressurized conditions that force the gas to stay in blended into the liquid—in solution. As soon as the bottle or can is opened, however, the pressure is reduced, allowing some of the gas to escape from solution—and turn into fizzy carbon dioxide bubbles! Pouring the soda into a glass releases even more bubbles. But how can this process lead to dancing candy?
Conversation hearts—common gifts for Valentine's Day—are denser than soda, so if they're placed in a glass of soda, they will fall to the bottom. But what happens next? Try out this science activity to find out!

  • At least four conversation hearts
  • A fresh bottle or can of colorless soda (unopened), such as Sprite or 7-Up
  • A tall, clear glass
  • Get out your unopened soda, the glass and four conversation hearts.
  • Place everything in an area near a sink in case your soda overflows.
  • Fill the glass nearly to the top with the fresh soda.
  • Take the four conversation hearts and drop them, one at a time, into the soda. What happens when you drop the hearts into the soda?
  • Watch the soda for a few seconds. What happens to the conversation hearts shortly after they've been dropped into the soda?
  • Watch the soda for at least five minutes more. What happens to the conversation hearts in the soda over time?
  • Can you explain the behavior of the conversation hearts in the soda? How do you think carbon dioxide gas is involved?
  • Extra: Try this science activity again but this time use other candies. Do you get the same results with other candies? If they do not "dance," why do you think this is?
  • Extra: Instead of using soda, try using water with vinegar and baking soda, which will also create carbon dioxide gas. Specifically, try filling a glass about half full with water, mix in one teaspoon of baking soda, add the conversation hearts and then slowly add vinegar until the glass is nearly full. Do the conversation hearts "dance" in the baking soda and vinegar mixture?
  • Extra: Another fun way to explore carbonation is to try out the Spurting Science: Erupting Diet Coke with Mentos Bring Science Home activity. How are the two carbon dioxide–based reactions similar? In what ways do you think are they different?

Observations and results
Did the conversation hearts first sink to the bottom of the glass but then, over time, float back up—and then down again—in the soda, "dancing"?
In this activity you dropped conversation hearts into a glass of freshly poured, carbonated soda. Because the conversation hearts are denser than soda, they should have quickly fallen to the bottom of the glass. But then something interesting should have happened. After a couple of minutes, some (or all) of the four candies should have slowly begun to rise up through the soda. The carbon dioxide bubbles in the soda were sticking to the candies, and when enough lighter-than-soda bubbles accumulated on a given candy, they should have lifted it up through the soda. Once at the top of the soda the carbon dioxide bubbles could escape into the air, causing the candy to sink once again. But as the candy sank, more bubbles should have stuck to it, causing it to rise again and repeat the cycle. This up-and-down motion makes the conversation heart candies appear to slowly "dance" in the soda.
More to explore
Dancing Raisins, from the University of Wisconsin–Madison
Coke & Mentos—Exploring Explosive Chemistry!, from Science Buddies
Science for Kids: Carbonation, from AllExperts
Science Activities for All Ages!, from Science Buddies

This activity brought to you in partnership with Science Buddies