1. Limewater can be used as a testing solution for the existence of carbon dioxide.
  2. When carbon dioxide mixes with limewater, the limewater turns cloudy


  • lime (used in making pickles)
  • water
  • tablespoon
  • 2 glass quart jars with lids




  1. Fill one of the quart jars with room temperature water.
  2. Add 1 tablespoon of lime, and stir.
  3. Secure the lid.
  4. Allow the solution to sit overnight.
  5. Pour the clear liquid floating in the jar into the second quart jar. Be sure not to pour any of the lime that has settled on the bottom of the first jar into the second jar.
  6. Put the lid on the second jar. This is limewater and can be used in experiments to test for the presence of carbon dioxide.


  • The liquid is milky white and opaque (light does not pass through it) at first. The particles of lime that are not dissolved are temporarily suspended in the water, making it appear milky and opaque. After time, particles of lime start to precipitate (clump together and fall downward). After standing overnight, the clumped particles fall to the bottom of the jar. The clear liquid is limewater. It must be covered to prevent carbon dioxide that is in the air from dissolving in it.

Assessment Ideas

  • Devise a way to use limewater and carbon dioxide to write secret messages to friends. You can make carbon dioxide gas by mixing baking soda and vinegar.


  • Chemistry: Use the limewater in experiments to test for the presence of carbon dioxide. Some of the following activities will utilize the limewater. Can you think of any other experiments to use the limewater?


  • lime: a white substance also known as calcium oxide (CaO). When mixed with carbon dioxide, CO2 , the following chemical reaction takes place: CaO + CO2 = CaCO3 ("calcium carbonate"). Therefore, when limewater comes into contact with carbon dioxide, calcium carbonate is precipitated. That is why the limewater turns cloudy.
  • precipitate: the condensing or combining together of chemical constituents. The condensed product is heavier than its surroundings. Therefore, it falls downward (like raindrops).


  • "Winds of Change" educational CD-ROM, Copyright Caltech and NASA/Jet Propulsion Laboratory