Don't you love it when your school curriculum goes along with a real life experience at the same time? We did a chemical reaction experiment with vinegar (our acid) and baking soda (our base) to blow up a balloon. The kids enjoyed watching as it changed into CO2.
After the balloon was filled up they quickly realized that their balloon didn't weigh the same as a balloon with air from our mouths. Why? CO2 is heavier than air. The balloon didn't float down to the ground, it came down much faster.
Well, it just so happens that we did some filming this weekend with a smoke machine and to do that we had to have dry ice (which is a solid form of CO2). Why does the smoke go low? Again, CO2 is lighter than air.