If you’ve ever burped, you know that it’s a lot easier to do after chugging an entire soda. Now why is that?

Soda is loaded with gas bubbles — carbon dioxide (CO2), to be specific. And at standard temperature (68oF) and pressure (14.7 psi), carbon dioxide is a gas. However, if you burped in Antarctica in the wintertime, it would begin to freeze as soon as it left your lips. The freezing temperature of CO2 is -109oF, and Antarctic winters can get down to -140oF. You’ve actually seen this before, as dry ice (frozen burps!).

Carbon dioxide has no liquid state at low pressures (75 psi or lower), so it goes directly from a block of dry ice to a smoky gas (called sublimation). It’s also acidic and will turn cabbage juice indicator from blue to pink. CO2 is colorless and odorless, just like water, but it can make your mouth taste sour and cause your nose to feel as if it’s swarming with wasps if you breathe in too much of it (though we won’t get anywhere near that concentration with our experiments).

The triple point of CO2 (the point at which CO2 would be a solid, a liquid, and a gas all at the same time) is around five times the pressure of the atmosphere (75 psi) and around -70oF. (What would happen if you burped then?)

What sound does a fresh bottle of soda make when you first crack it open? PSSST! What is that sound? It’s the CO2 (carbon dioxide) bubbles escaping. What is the gas you exhale with every breath? Carbon dioxide. Hmmm … it seems as if your soda is already pre-burped. Interesting.

We’ll actually be doing a few different experiments, but they all center around producing burps (carbon dioxide gas). The first experiment is more detective work in finding out where the CO2 is hiding. With the materials we’ve listed (chalk, tile, limestone, marble, washing soda, baking soda, vinegar, lemon juice, etc. …) and a muffin tin, you can mix these together and find the bubbles that form, which are CO2. (Not all will produce a reaction.) You can also try flour, baking powder, powdered sugar, and cornstarch in place of the baking soda. Try these substitutes for the vinegar: water, lemon juice, orange juice, and oil.


  • baking soda
  • chalk
  • distilled white vinegar
  • washing soda
  • disposable cups and popsicle sticks
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37 Responses to “Hidden Carbon Dioxide”

  1. Great job! The chalk melts because vinegar reacts with the calcium and removes it from the chalk as it makes CO2.

  2. leeann_brodeur says:

    Hi!..i did it! me and E’LYSE did the 1 thing but…expect the washing soda part…we did not have washing soda…but we did have baking soda and it did work! we had put b-a soda and vinegar and guens what? …big bobbles
    and then little bobbles went up.The next one…we had put vinegar and chalk but it did not take long! it went like 5 secondes! and the next one was…a littte varnegar and then baking soda and chalk! and I know the third was really different but we did not have the lass thing.but it was really fun and i just love it… thank you… and why to the chalk melt?bye! adele.

  3. Yes, along with nitrogen and oxygen. Not all the oxygen is converted to CO2 with every breath (that’s why people breathe into a paper bag when they hyperventilate don’t suffocate initially).

  4. Brook Batzel says:

    dont we breath out carbon dioxide?

  5. Yes, about 20% of the air you inhale is oxygen and about 4-5% of that oxygen gets converted to CO2 with every exhale

  6. Brook Batzel says:

    We exhale carbon dioxide! isn’t that right? EVERYBODY does!

  7. Mary Legreid says:


  8. Wow – that’s unusual and interesting! What kind of vinegar did you use? It reminds me of the popcorn rock experiment here: https://www.sciencelearningspace2.com/2013/09/popcorn-rock/ The scientist in the 1980s that figured this out was using acid to dissolve the limestone to get at the fossils inside, and instead of dissolving, it combined with the minerals in the rock and formed crystals!

  9. Bonnie Telesmanich says:

    When we put our chalk into the vinegar to sit, the next day the chalk had soaked up vinegar all the way to the top and started growing crystals. We left it there and got a really neat crystal formation.

    I know there is calcium in chalk so do you suppose that is what the crystals are made of?

  10. Yes they are taped on the top. And pouring does take practice – you need to pour further back than you think. Keep trying!

  11. Evangeline Gregory says:

    Also I tried pouring the gas into the cup,and well…. nothin’ happened.

  12. Evangeline Gregory says:

    How did you get the top skewer on the long pencil and keep it there without it falling off? Did you use tape?

  13. Crystal Burling says:

    This is so cool. You make the most fun science projects ever Aurora!

  14. Yes it might, depending on how sensitive it is. I have one here in my ab that registers a change in reading just by walking past it or breathing on it, so that would definitely work. Keep in mind that gases are really hard to measure due to how they swirl and expand, and you’ll just get an indicator reading, not an absolute measurement.

  15. Melissa Vander Broek says:

    We have been trying the experiment but we were wondering if a digital sensitive scale will work?

  16. You must be logged in before accessing the downloads. If you still have trouble, let me know and I’ll get my team to look into your account.

  17. Christie Laing says:

    We are unable to open the link for the exercise/w’sheet

  18. Caroline Wood says:

    these bubbles in the test tube, what are they made of? Carbon dioxide?

  19. Laura Todd says:

    You also spoke about stirring them but you never did in the video. What scienfically will happen then?

  20. Laura Todd says:

    1. I understand that this is a chemical reaction. Does that mean that the sodium bicarbonate mixed with vinegar change into carbon dioxide or does it mean that when these 2 meet the side effect is carbon dioxide? When reading all the introductory information you stated that the changing of the protons in matter is what changes it’s elements. Like when you talked about iron changing to gold. That example was from one element to another. This experiment is different. Right? or am I getiing all of this confused?

    2. When i change the liquid to water or oil I am assuming they will not create carbon dioxide. Is that because they are not acidic? What shall I explain to the boys is happening there?

  21. You’ll want to practice ‘pouring’ and this is best done over a lit candle. Gently pour out your invisible CO2 gas over where you think it should go in order to snuff out the candle – this will tell you if you’re on target or not. Most folks find they’re pouring way off-center! After you’ve snuffed the candle several times, do this again but now aim for your cup on the scale and pour super-slowly so it doesn’t slosh out. It’s a touchy experiment because you can’t see what’s happening!

    Well, to be honest, there is a way to see it, but that involves using a special lighting technique I used back in college that is super-sensitive to the different density regions of air. I wonder if I could figure out a way to show you how to build the same set up I had in my PhD lab with regular household stuff, so you could see what you’re doing? Hmmm… I’ll put that on my lab list… 🙂

  22. We started the Unit 8, Chemistry and today tried the experiment in which we weigh CO2 by pouring it into a cup on our homemade scale. We tried several times, but it did not work. We tried making differing amounts of vinegar/baking soda and different size containers. We also tried to adjust our scale so that it would be ultra sensitive. No luck. I am wondering two things. What could have gone wrong?

  23. Lori Miller says:

    Wow that was quick. Thanks for getting back to me. I saw some information about Iodine affecting hormones. Love to read this one.

  24. Sure – what kind of info are you looking for? The MSDS will tell you all about safe handling, storage, and disposal. Wiki will tell you about the history and what it is in everyday English.

  25. Lori Miller says:

    Hi Aurora,
    I was looking for the information about Iodine. Can’t seem to find it. Can you help me to find it?

  26. Never thought you’d have questions about burps, did you? 🙂

    1. CO2 is cheap to make and non-toxic (the gas, not the explosive force it creates), so they stuff as much as they can into cartridges. You can really use almost any compressed gas and get similar results, like nitrogen or oxygen if it was possible.

    2. Dry ice (and water ice) is a great insulator of heat (like a thermos), so if you have a lot of it, it will keep itself cold. For hundreds of years, people used this idea for their ice houses – they would keep large cut blocks of water ice (from winter) and cover it with straw in a special no-window house and it would stay as ice all through summer.

    3. The combination of salt/sugar/baking soda:

    There is a difference between baking soda and baking powder. Baking soda is sodium bicarbonate, and reacts when combined with something acidic (you’ve seen this when you add it to vinegar). It makes lots of CO2 bubbles which cause your cookies to rise. You always add it near the end of the recipe, just before putting it in the oven because it start to react as soon as you add it to your mixture.

    Baking powder contains baking soda and lots of other things, including cream of tartar and starch. (Single-acting baking powder start reacting when it comes in contact with wet things, like cookie dough and bread, so you have to add it at the very end before you bake it (or all the gases are released and your cookies stay flat). Double-acting baking powder reacts twice (there’s a built-in delay) so the cookie dough will rise a bit initially, but much more the second time (hopefully in the oven!)

    Read more about the chemical reaction in cookies here.

  27. Kelly Kaiser says:

    Very cool! We have several CO2 questions for you that came to mind when we did this experiment. 1) Our son does shooting sports and wants to know why they use CO2 cartridges vs pressurized oxygen cartridges in their air rifles? 2) How do they keep dry ice as cold as it needs to be at the grocery store? 3) What is actually happening scientifically when you bake cookies/cakes that call for baking soda/powder?

  28. Leah Brooks wrote: “We tried the CO2 balance experiment twice and it didn’t work. We used small cups (Dixie cups). Perhaps they weren’t big enough? We had a very sensitive scale. Any thoughts?”

    Sometimes when you pour the CO2, you actually miss the container (this is the most common problem people have with this experiment!). Because you can’t see the CO2, try pouring onto a lit candle and watch for it to snuff out… this will tell you if you have CO2 or just air in your container. The candle will also help you aim the invisible gas in the right place until you get the hang of how to pour it out of the container. Let us know how it goes!

  29. Sachin Aradhey says:

    I think that the CO2 experiment was cool and I never knew that CO2 was heavier than air!

  30. Leah Brooks says:

    We tried the CO2 balance experiment twice and it didn’t work. We used small cups (Dixie cups). Perhaps they weren’t big enough? We had a very sensitive scale. Any thoughts?

  31. Megan wrote: “Where can we find washing soda? I cannot find it anywhere?”

    You can find washing soda here or just use baking soda.

  32. Megan Osborne says:

    Where can we find washing soda? I cannot find it anywhere?

  33. Meredith wrote: “Hi! My son is loving the chemistry! He wants to comment that the baking soda formed chunks when left in the vinegar. Why did this happen?”

    NaHCO3 is the chemical name for baking soda, where the C = carbon, H = hydrogen, O = oxygen, and Na = sodium. When you add water, the sodium and bicarbonate split apart into ions (Na+) and (HCO3- ) like this: NaHCO3 —> Na+(aq) + HCO3-(aq)

    Distilled vinegar is also known as acetic acid, and is written like this: CH3COOH and it also splits into hydrogen ( H+) and acetate ions (CH3COO-): CH3COOH H+(aq) + CH3COO-(aq)

    When you mix baking soda and vinegar, you actually are doing two different chemical reactions – one of which involves the hydrogen ions (H+) joining up with the bicarbonate ions (HCO3- ) to make the carbonic acid molecule (H2CO3), which are the chunks you find at the bottom of the cup. If you wait awhile, you allow the smaller bits to fall out and gather together in the solution. This chemical is used to make the bubbles in soda… and also for gas exchange in your blood. Cool, huh?

  34. Meredith Hutter Chamorro says:

    Hi! My son is loving the chemistry! He wants to comment that the baking soda formed chunks when left in the vinegar. Why did this happen?