How to Make a CO2 Sandwich

Zipper-lock Bag Variation

1. Start by putting on your safety glasses.
2. Fill three quart-size zipper-lock bags with approximately 1 tablespoon of baking soda.
3. Fill three snack-size zipper-lock bags with varying amounts of vinegar.  For example, fill one bag with 60 mL (1/4 cup) of vinegar, the next bag with 80 mL (1/3 cup) of vinegar and the last bag with 120 mL (1/2 cup) of vinegar.
4. Seal the vinegar bags and place them in the bags with the baking soda. When you seal the outside bags, make sure to remove as much of the air as possible.
5. Put the bags on a table where it's okay for things to get a little wet and messy (outside tables would be good).
6. Now get ready for the fun... Punch the vinegar bags inside the baking soda bags to break them open and then shake the baking soda bags to make sure the substances mix.
7. Make observations about how large each bag gets and how long it takes before you hear the giant POP!

Toilet Paper Variation

1. Tear off a square of toilet paper.
2. Place 1 tablespoon of baking soda in the middle of the toilet paper square.
3. Twist or fold the toilet paper around the pile of baking soda making a small packet.
4. It’s best to have someone help you with the next few steps. Open the quart-size zipper-lock bag and measure 1/4 cup of vinegar into the bag. Add 1/4 cup of warm water to the bag.
5. Zip the bag closed, but not all the way. You want a small opening just large enough to sneak in the wrapped up baking soda.
6. IT'S TIME FOR A FIELD TRIP. Move the experiment to the sink, or better yet, OUTSIDE! Remember, it’s all about teamwork. Drop the baking soda bundle into the bag and quickly seal the bag closed. Place the bag on the ground (or in the sink if you’re indoors) and get out of the way. Watch closely as the bag begins to puff up… it gets bigger and bigger until… BAM! Pop goes the sandwich bag.

How does it work?

Sure, bubbling liquids and popping bags are fun, but what’s the science behind the exploding lunch bag? When you mix vinegar and baking soda, a chemical reaction takes place producing a gas called carbon dioxide (CO₂). If you really want to impress your friends, use the chemical names for each of the ingredients. Acetic acid (that’s vinegar) plus sodium bicarbonate (baking soda) produces carbon dioxide gas and water. The bag puffs up because the carbon dioxide gas takes up lots of space, eventually filling the bag. If there’s more gas than the bag can hold… KABOOM! If you’re lucky, the zipper-lock seal will bust open, but the bag will not break. Now you can reuse the bag to make another CO₂ sandwich. Wrapping the baking soda in tissue paper or separating the substances in bags is a clever way of slowing down the reaction.

Additional Info

Science Fair Connection:

The CO₂ Sandwich activity makes a good science fair project because it contains a variable, or something that changes in the experiment. You know that mixing baking soda and vinegar creates a reaction that eventually causes the zipper-lock bag to pop. If you demonstrate that first and then change something, you can compare the results and show the effect of the change on the explosion. 

• Change the amount of vinegar you use, but be sure to keep the amount of baking soda (one tablespoon) and the size of the zipper-lock bags the same. 
• Change the amount of baking soda but keep the amount of vinegar and the size of the zipper-lock bags the same.
• What would happen if you diluted the vinegar with a little water? How would this affect the expanding gas?
• Examine how the temperature of the water affects the pop.
• Wrap the baking soda in two or three pieces of tissue. How will this affect the reaction?

Remember, in a good science fair experiment you are only allowed to change one variable at a time. What are three more variables you could change? By changing only one variable at a time, you’ll be able to determine which ingredient has the most impact on the POP!