Limewater Carbon Dioxide Test

(Chemistry for ages 8+)


Chemical reactions are happening all the time and everywhere! They happen inside your body, when you cook food, and when a car is driven. Chemical reactions can even be helpful for identifying substances in the environment, like using limewater to test for carbon dioxide, which is what the video above shows. Below, we’ve outlined how to make limewater and what you’ll need to do this activity.


Calcium hydroxide (slaked lime)
Water (distilled is recommended but tap water will work)
Large jar or bottle (up to 1 gallon)
Filter paper
2 small jars or glasses
Adult supervision


**Day before preparations

  1. Add 1 teaspoon of calcium hydroxide (slaked lime) to the large jar or bottle.
  2. Fill the bottle with distilled water and stir or shake (if your jar has a lid) vigorously for 1-2 minutes. Let stand undisturbed for 24 hours.

**Day of procedures

  1. After 24 hours, using the filter and filter paper, strain the lime sediment out of the water. Be careful not to stir it up beforehand.
  2. The limewater should be clear, so if it is still cloudy after the first filtration, repeat step
  3. Once the limewater is clear, you are ready to test for carbon dioxide. Add some limewater to one of your smaller jars. Do not fill the jar more than half full.
  4. Fill your other small jar half full with regular water (distilled or tap).
  5. Using the straw, exhale (blow bubbles) in the glass with limewater. Be sure to not blow too hard to avoid splashing, and do NOT suck the liquid up the straw! What do you see happening to the limewater?
  6. Next, repeat step 7 with the regular water. Does anything happen when you exhale into the regular water?



When we breath, we inhale oxygen, chemical reactions happen in our lungs to use the oxygen for our whole bodies, and we exhale carbon dioxide. Blowing into the straw puts carbon dioxide into the water, and when lime is present, more chemical reactions happen and calcium carbonate is created.

Calcium carbonate (the same stuff that is used to make chalk) is what turns the limewater white and cloudy. Because regular water does not have lime, there is visible change that happens when you exhale into it.