Heres What You Will Need;
Balloon, backing soda, vinegar, and a bottle.
First Step.
Take the balloon and fill it up with baking soda fill about half the balloon.
Next.
Put vinegar about half way full in the bottle.
Following.
Put the balloon over the lid of the water bottle and let the baking soda drop into the bottle.
Lastly.
Watch the balloon fill up with co2.