Carbon Dioxide Tests: Part I. Limewater

    Kids, here you will make a solution that can test for the presence of carbon dioxide (CO2 ) gas. This is a two-part project. Save the limewater you make for use in the next issue of ChemShorts. You will need two glass quart jars with lids, a tablespoon, and lime (CaO, the substance used in making pickles, not the small green citrus fruit). Fill one jar with water. Add one tablespoon of lime and stir. Secure the lid and allow the solution to stand overnight. Pour off the clear liquid into the second jar very carefully, do not let any of the settled lime sneak in. Keep the jar of clear limewater closed until needed.

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    At first the liquid should be milky white and opaque. Opaque means that light cannot pass through, making the solution impossible to see through. The milky appearance is due to undissolved particles of lime that are temporarily suspended in the water. It takes time for all of these particles to settle down. The resulting clear liquid contains as much dissolved lime as it can hold before settling out. This is called a saturated solution. It is similar to dissolving Kool-Aid or lemonade crystals in water. When too many crystals are used, the extra settles out on the bottom.

    The jar must be kept tightly closed so that carbon dioxide from the air won't dissolve in it. We have other plans for this solution.

    (Notes: Do not let anyone drink this solution and let an adult partner handle the lime for you).  


    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    November 1992