Baking soda + vinegar.
This well known reaction that is so enjoyed by kids and kids at heart, can be used to teach several basic science concepts. Not just a cool science trick, this Instructable will walk you through how to set up a science lesson to explore several concepts.
The takeaway of this experiment that a gas is a state of matter that can only been seen in certain situations; and the question to end it all is whether CO2 gas is heavier or lighter than air?
Step 1: Ingredients and Materials
Balloon (or two)
Narrow mouthed bottle
Baking soda (~2-3 Tbs)
Vinegar (~4 oz)
Observant eyes and curious disposition
Step 2: Optional: Introduce the Experiment
If you're doing this with students, here's how you can introduce this experiment. *Note: to do this, it's best to have another small, unmarked container of the baking soda, so they can see it (vs in the balloon).
- We're going to be mixing a solid and a liquid. These are two different states of matter; what is the third? (Gas). Optional: What are the characteristics/properties of the different states of matter?
- Show the bottle with the liquid in it and the unmarked container for the baking soda. Here are our two things that we'll be mixing. Let's make some observations about these things to try to identify them. You may smell them, but it's important not to sniff an unknown substance, especially in science, but to waft. You can learn how to waft here. Let the students try to figure out what the two substances are.
- What are the two substances and how do you know? Vinegar and baking soda.
- What happens when we mix this solid and liquid together? If any students have seen this, they'll probably describe fizzing or bubbling. Once they reach this prediction, you can confirm that they will see bubbles and fizzing, and that that is CO2 gas that will be created from the reaction.
- This CO2 gas will fill/blow up the balloon. While we can't see the gas itself, we can see the gas bubbles in the vinegar and we know it's there because it will blow up the balloon.
- After the reaction, we'll tie off the balloon and then we'll answer the question "Is a CO2 filled balloon lighter or heavier than air? (In other words, will it sink or float?)
Step 3: Setting the Materials Up
- Pour some vinegar into the bottle. ~4 oz of liquid, or 1/4 of the bottle's capacity is enough.
- Put about 2-3 tablespoons worth of baking soda into the balloon via the funnel and spoon.
- Place the mouth of the balloon over top the bottle without allowing any baking soda to fall in yet.
Step 4: The Reaction!
Have fun with this part. You may need to hold the neck of the balloon on the bottle opening, so it doesn't blow off. Lift the balloon to empty the contents into the bottle and enjoy!
Step 5: Wrapping It Up
The active bubbling should calm down within the minute, but student will still be able to observe gas bubbles rising in the vinegar for a few minutes after. This is one situation in which you can see gas (the bubbles). What is the other evidence of the gas being produced? The balloon being blown up.
After you take the balloon off and tie it up, you can hold it up in the air and remind students that they're about to find out if a CO2 filled balloon is lighter or heavier than air. (It's heavier).
For those interested, here's the chemical equation:
NaHCO3(s) + CH3COOH(l) → CO2(g) + H2O(l) + Na+(aq) + CH3COO-(aq)
with s = solid, l = liquid, g = gas, aq = aqueous or in water solution.
Another common way to write this reaction is: NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2