You will need:

An empty glass or plastic bottle (check your recycling - try with different sized openings and see what happens!), a balloon, a spoon, about a cup of vinegar and about 1/3 cup (or about 6 teaspoons full) of baking soda.

Step 1: The Vinegar

Fill your bottle with 1 cup of white vinegar. Vinegar is very acidic.

Step 2: Fill the Balloon

Fill your balloon with about 6 teaspoons of baking soda (you can create a little funnel by rolling a small piece of paper tight on one end and wide on the other, or you can ask a parent or sibling to stretch the top of the balloon open wide while you fill it).

Step 3: Stretch the Balloon

Stretch the top of the balloon securely over the top of the bottle. The weight of the baking soda in the balloon will cause it to hang over to the side.

Step 4: Get Ready for the Reaction

When you’re ready, have someone hold the stretched part of that balloon onto the bottle just in case you have a SUPER successful chemical reaction!

Step 5: Watch What Happens!

Ready? Now pick up the bottom of the balloon and dump that baking soda right into the vinegar all at once and behold! When you add a base (in this case baking soda) to an acid (the vinegar) it causes a chemical reaction that releases carbon dioxide… which, yup, you guessed it - fills your balloon! You may have to hold the balloon upright as it fills to allow a clear path for the carbon dioxide to pass through.

Note: The smaller the opening of the bottle, the smaller the amount of carbon dioxide can get through to the balloon and the more gradually the balloon is filled. We used a bottle with a wide mouth which allowed a greater amount of carbon dioxide to shoot up into the balloon at a much faster rate (hence the need to hang on!)

Find this science experiment and more ideas in our 64 Easy Science Experiments for Kids article or peruse our STEM Guide for Kids for more hands-on experiments.