Scientific observations of different balloons

I promised J some science after naptime. I decided to nap too instead of prepare a science lesson. He awoke pretty excited, so I asked him what kind of science he wanted to do. Since he was close to our stored, small helium tank while waking me up, he pulled that out. Not wanting to repeat the hover balloon lesson, I had to think of something else with balloons on the fly (which is harder to do in a sleepy stupor and with preggo brain). It's also been bothering me from the scientific standpoint that a post is going around Pinterest saying that our baking soda + vinegar reaction blowing up a balloon is a good alternative to helium.

I decided that we should play with the weight of the balloons and that this could be a good lesson for J in making hypotheses (educated guesses about what he thinks will happen when conducting the experiment).

Objectives:
*To determine what three different balloons will do: sink or float. The three balloons would be filled with 1. air (blown up with our mouths); 2. helium; 3. carbon dioxide (CO2) which is the gas product of the chemical reaction between baking soda and vinegar.
*To determine which gas is heavier: air, helium, or carbon dioxide.

J's Hypotheses:
*Hypothesis 1:
     1. Air will sink.
     2. Helium will float.
     3. Carbon dioxide will sink.
*Hypothesis 2:
     1. Air is heavier than carbon dioxide.
     2. Helium is lighter than air.

Experiment:
*Fill 1 balloon with air from your mouth.
*Fill (or obtain) 1 balloon with helium.
*Conduct the baking soda + vinegar reaction (see link above) and tie off the balloon once it's full of carbon dioxide gas.
*Hypothesize about what the balloon will do when dropped: sink or float?
*Drop each balloon and observe what happened.
*Make conclusions on your observations: where your guesses correct?
*Now using what you just learned from your balloon dropping observations, make hypotheses about which balloon is heavier or lighter.
*Weigh the balloons on the scale/balance (like the one we used in our balance game), or create your own balance from office supplies.

Results:

*Helium floated.

*Air balloon sank.

*Carbon dioxide balloon sank.

*Air balloon is heavier than helium:

*Carbon dioxide balloon is barely heavier than the air balloon, but it is also smaller.

*The air balloon is slightly heavier than a deflated balloon (but not by much).

Discussion:
*There is a difference in balloon volume between the air and the carbon dioxide. We didn't have a large enough reaction to really blow the balloon up to the same size as the one we blew up with our mouth. Even with a smaller balloon volume, the carbon dioxide balloon is heavier than the balloon we filled up with our air.
*It's also important to note that carbon dioxide is a product of what we exhale when we breathe (or blow up a balloon). However, there are a lot of other gases mixed in with the carbon dioxide.
*We couldn't figure out a good way to measure the weight of the helium, so we tied it to the scale, which immediately raised the scale on the side of the helium balloon, but helium is lighter than air.

Some other fun we had:
*We played, what can we tie the helium balloon to in order to keep it from floating to the ceiling.
     - We ended up using a Cootie Bug.

After the experiment, J thought it would be fun to launch balloons with our balance/scale.
     - I always recommend well-supervised free play time after experiments.
     - Kids are awesome at finding fun new ways to explore their world.
     - Don't forget to explain what's happening as they make new discoveries.