When raisins are added to a solution containing water, baking soda, and vinegar, why do the raisins dance? — RE, Troy, IL
Baking soda and vinegar react in water to release carbon dioxide molecules. If the chemicals are sufficiently dilute in the water, the carbon dioxide molecules may remain dissolved in the water almost indefinitely. But when the water has impurities in it, the carbon dioxide molecules tend to come out of solution as gas bubbles at those impurities. The impurities allow the molecules to form tiny gas bubbles—a process called nucleation. In the present case, the raisins serve as the impurities that nucleate gas bubbles. As the gas bubbles grow on the surfaces of the raisins, the raisins experience upward buoyant forces from the surrounding water. The bubbles float upward, carrying the raisins with them and causing the raisins “to dance.”