Limewater test for carbon dioxide

Limewater is a clear aqueous solution of calcium hydroxide. It can be used to test whether a gas contains carbon dioxide.

To carry out the test, bubble the gas through limewater or shake the gas with it. A positive result is that the clear limewater turns milky or cloudy.

The change occurs because carbon dioxide reacts with calcium hydroxide to form calcium carbonate. Calcium carbonate is a fine solid precipitate that makes the mixture look cloudy.