Fourth graders observe what is happening when an Alka-Seltzer tablet is placed in a clear cup of water. They observe the release of carbon dioxide gas. Pupils answer the question of how much as is released by observing the experiment with the lid on the reaction and see if it makes enough gas to pop off the top. Students observe for a third time, but only a half of tablet is used. They answer the question which lid popped off the furthest in the air?