The limestone cycle Limestone
Learning Objectives By the end of the lesson I will be able to: • Carry out thermal decomposition of calcium carbonate • Draw a flow diagram of the limestone cycle • Write balanced chemical equations for reactions in the limestone cycle
Heating limestone • When limestone (calcium carbonate) is heated, it breaks down (decomposes) • When something breaks down with heat we call this reaction… Thermal decomposition • Calcium carbonate breaks down into calcium oxide (quicklime) and carbon dioxide
Thermal decomposition of limestone Calcium heat calcium carbon Carbonate oxide dioxide CaCO3heatCaO CO2
Reacting quicklime with water • Calcium oxide (quicklime) is a strong alkali • It reacts with water to form calcium hydroxide Ca(OH)2 • Calcium hydroxide is also known as slaked lime
Making cement, mortar and concrete. Decomposing rotting bodies in mass graves and reducing the smell ! Uses for quicklime
Making Slaked Lime calcium + water calcium oxide hydroxide CaO + H2O Ca(OH)2
To neutralise acidic soils, and to break up the soil so that plants can grow well To neutralise lakes which have been polluted by acid rain Uses for slaked lime
Limewater • Limewater is a solution of calcium hydroxide • It is used to test for carbon dioxide • We breathe out a lot of carbon dioxide • If we blow through a straw into limewater it will change from clear to milky-white • The substance formed in this reaction is insoluble calcium carbonate
Testing for carbon dioxide calcium + carbon calcium + water hydroxide dioxide carbonate Ca(OH)2 + CO2 CaCO3 + H2O
The Limestone Cycle These reactions all make up the limestone cycle.
Task: Use the worksheet called ‘The Limestone Cycle’ - fill in the gaps and complete the equations for the reactions of limestone. Stick into your books.
The Limestone Cycle limestone carbon dioxide heat quicklime limewater more water water Slaked lime