There are a lot of really fun experiments that involve vinegar and baking soda. Things like exploding sandwich bags and of course erupting volcanoes. We love them because they are easy to do and generally create a nice big mess that kids can’t resist. But this little experiment, using baking soda and vinegar to inflate balloons is one of my own favorites because there is an extra layer of science we can talk about after the fun is over. That’s right we get to talk about molecular weight!!
Baking Soda and Vinegar Balloon Inflator
- an empty bottle – about 500 ml. Either glass or plastic is fine but just make sure a balloon can fit over the mouth
- a balloon
- a funnel. If you don’t have one you can make one by rolling a cone shape from a piece of paper
- 4 ounces of vinegar
- 2 tablespoons of baking soda
Pour the vinegar into the bottle.
Using the funnel, put the baking soda into the balloon.
Carefully fit the balloon over the mouth of the bottle being careful to not yet dump the baking soda into the bottle.
Now, being sure to hold the balloon firmly around the mouth of the bottle, dump the baking soda into the bottle. Keep holding it tightly as the balloon starts to inflate!
When the balloon is done inflating carefully remove it and tie it.
How does it work?
I’m pretty confident that by this point in your life you know that when you combine vinegar (an acid) and baking soda (a base) are combined they produce a reaction that creates a gas, that gas being carbon dioxide. In this experiment the balloon is capturing the carbon dioxide created and inflating. That’s all there is to it.
I often see this experiment go by on Pinterest telling people you can more or less create your own helium like gas at home to blow up floating balloons for parties. Obviously that’s impossible. Why? Because molecular weight matters. If you look at the periodic table of elements you will see that the only gas lighter than helium is hydrogen. Of course carbon dioxide, being a compound (one carbon and two oxygen), isn’t on the periodic table but we do know it’s weight and it’s heavier than helium – much heavier. Helium has a molecular weight of 4 (kg/kmole) and carbon dioxide has a molecular weight of 44. That’s a huge difference. And the approximate molecular weight of dry air is about 28 so you can see why balloons filled with helium float and those filled with carbon dioxide just simply cannot.
If you have an extra balloon lying around go ahead and blow it up the old fashion way to the same size as the one you did in the experiment. Feel both balloons. Can you feel the difference in weight? You probably can although it might not be huge. Even though we do exhale carbon dioxide we also exhale oxygen and nitrogen, both of which are lighter than carbon dioxide (but still much heavier than helium).