Measure a cup of water and have your child pour it into a tall, clear glass. Help him add a tablespoon of baking soda, and have him carefully stir until it dissolves. Next, drop in 3 or 4 raisins. They’ll sink to the bottom. Then add ½ tablespoon of white vinegar — and watch those raisins dance! Explain that the baking soda and the vinegar have a reaction that creates a gas (carbon dioxide) that lifts the raisins up.