This neat little experiment comes from Science Bob.
You will need:
A glass or plastic bottle with a relatively narrow neck.
1 tbsp. of dry yeast
1 tbsp. of sugar
Blow up the balloon and then release the air from it to stretch a bit. Then, using the funnel, pour the dry yeast and sugar into the bottle and shake it all up with some warm water. Put the balloon over the neck of the bottle, making sure it’s firmly in place.
After a few minutes, the yeast will begin making foam and the balloon will start to blow up because of carbon dioxide emission. The foam may actually overrun the top of the bottle and escape into the balloon – that’s OK.
A couple of hours later, the yeast activity will fizz out, but the balloon will retain its size.
It’s a very easy, fun experiment which prompts interesting discussion with kids about micro-organisms, metabolic processes and properties of gas.