In this activity, students heat limestone (mainly calcium carbonate) to form lime (calcium oxide) and note the differences between the reactions of limestone and lime with water, acids and carbon dioxide. Adding water to the lime produces slaked lime (calcium hydroxide) in an exothermic reaction. Some of the calcium hydroxide dissolves in the water, producing an alkaline solution called limewater. Students discover that on blowing into this solution through a straw, the calcium hydroxide solution reacts with the carbon dioxide in exhaled breath to form a cloudy precipitate of calcium carbonate (this is the basis of the limewater test for carbon dioxide). In effect, they have regenerated the original limestone. Continuing to blow through the straw for some time will result in the calcium carbonate precipitate re-dissolving as soluble calcium hydrogen carbonate. The site offers directions for students and teachers, a list of materials, information on the use and production of limestone in Great Britain, and a glossary.
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