Reactions Experiment!

Today Kindergarten students tried another chemistry experiment: "Reactions and Jumping Raisins".  It was pretty exciting to see what can happen when you combine certain substances like vinegar and baking soda.  The reaction between baking soda (sodium bicarbonate) and vinegar (dilute acetic acid) generates carbon dioxide gas which produced the "explosion" that happened in our first experiment.  

Next, we added the raisins.  What would happen? As we observed the raisins, we noticed that they initially sank to the bottom of the glass. Next, they "magically" rose to the top of the beaker, and then sank again.  They were jumping up and down! What was happening?  The raisins sank to the bottom  of the beaker due to their density, but because raisins have a rough, dented surface, they are filled with air pockets. These air pockets attracted the carbon dioxide gas in the liquid, creating the little bubbles on the surface of the raisins.

The carbon dioxide bubbles increased the volume of each raisin. With a greater volume, the raisin displaces more fluid, which then applies more buoyant force, pushing the raisins upwards. At the surface, the carbon dioxide bubbles pop and the raisins’ density changes again. Then they sink back down to the bottom. The whole process is repeated, making it look as though the raisins are dancing or jumping!