Science Lab: Burping Balloon

Some caves are deep underground, and they don't have much oxygen. However, they do have a lot of carbon dioxide. But you don't know how much because CO2 has no smell. There is a simple test you can do, and it's similar to the following experiment.


What gas can put out a flame?


  • Adult

  • Measuring cup

  • Vinegar

  • Small bottle

  • Funnel

  • Balloon

  • Teaspoon

  • Baking sode

  • Clay

  • Wide jar

  • Small candle

  • Matches


  • Pour about 1¾ ounces of vinegar into the small bottle.

  • Slide the bottom of the funnel into the mouth of the balloon.

  • Pour one teaspoon of baking soda into the balloon. To make sure all the baking soda made it into the balloon, gently shake the funnel. Remove funnel.

  • Hold the neck of the balloon closed and let the balloon fall to one side to keep the baking soda from falling out. Stretch the mouth of the balloon over the opening of the bottle.

  • Now hold the balloon upright so the baking soda falls into the vinegar. What happens to the baking soda? What happens to the balloon?

  • Watch the chemical reaction until you don't see any more bubbles.

  • What gas do you think is inside the balloon? Make a guess.

  • Now flatten a piece of clay and put it at the bottom of the jar.

  • Place the candle firmly into the clay so it stands up by itself.

  • Ask an adult to light the candle. Let it burn for a while so that the candle is short.

  • With the adult's help, pinch the neck of the balloon to hold in the gas, remove it from the bottle, and place it at the mouth of the jar with the candle. Slowly let go of the neck.

  • What happens to the flame?


Mixing baking soda and vinegar causes a chemical reaction that creates carbon dioxide gas. Unlike oxygen, which makes a flame burn faster, and hydrogen, which also burns, carbon dioxide is used to put out fires. So when you released the balloon full of carbon dioxide, the candle flame went out.

It's important to always practice fire safety. Not all fires can be put out with just water. Make sure your kitchen has a fire extinguisher. It uses carbon dioxide to put out a fire.

In a deep underground cave, explorers called cavers will carry a butane lighter with them. If they are starting to have trouble breathing, they flick open the lighter and look at the flame. If the flame immediately goes out or doesn't appear at all, then they head straight back to the entrance. There is not enough oxygen in the cave for them to safely explore.


Draw a picture of your experiment and label each part. You are making a diagram. You can use this drawing to recreate the experiment.

What other acidic liquids could you use? Try lemon juice, orange juice, or grapefruit juice.

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