What Does a Limewater Test Indicate?

Many introductory chemistry classes feature the lime-water test.

A lime-water test is a chemistry test that shows the presence of carbon dioxide.

Facts

When introduced to carbon dioxide, lime water (calcium hydroxide), forms into chalk or limestone, turning the lime water a milky color. Mixing pure carbon dioxide with lime water makes the lime water milky white in moments.

Methods

Unlike oxygen, carbon dioxide extinguishes fire.

Most carbon dioxide is mixed with other gases, such as oxygen in air, but it still reacts to lime water. Leaving an open container of lime water out reveals carbon dioxide in air; the lime water turns chalky in about one week.

Another way to test for carbon dioxide is by burning something in a container; the flame goes out if carbon dioxide, and not oxygen, is inside. Because several gases besides carbon dioxide put out fire, and because this test checks only for carbon dioxide in its purest form, the lime-water test is more comprehensive.

History

Eighteenth-century Edinburgh chemistry professor Joseph Black first proved the existence of carbon dioxide and created the lime-water test. He exhaled into lime water to show his students the carbon dioxide in his breath and extinguished candle flames by pouring jars of carbon dioxide onto them.

References

• GCSEScience.com: Test for Carbon Dioxide Gas, CO2(g)
• PBS: Nova ScienceNOW--Capturing Carbon
• Centre for Distance Learning and Innovation: Unit 3: Physical Science--Chemical Reactions, Lesson
• Creighton University: Joseph Black; Bruce Mattson

Resources

• University of Arizona: Lime Water/Carbon Dioxide Reactions
• Creighton University: Microscale Gas Chemistry, Experiments with Carbon Dioxide; Bruce Mattson