and its uses

What is limestone?

• It is a sedimentary rock• It was formed mainly from

sea shells• It is the compound called

calcium carbonate• It is a useful raw material

What can limestone be used for?• Building walls

• Building houses

• Limestone is also used to make cement and concrete

• Neutralising excess acid in lakes or soils

More about limestone• Limestone is dug up out of the ground from

lime stone hills.• In Britain about 150 million tonnes of

limestone are used each year• Limestone is the compound calcium

carbonate• It’s formula is CaCO3

• Limestone can be chemically changed into other things

Heating limestone• When limestone (calcium carbonate) is heated,

it will break down (decompose)• When something breaks down with heat we

call this reaction a ….Thermal decomposition reaction

• Calcium carbonate will be broken down into calcium oxide and carbon dioxide on heating.

• We call calcium oxide quicklime

Equation for this reaction

Calcium heat calcium carbon

Carbonate oxide dioxideCaCO3(s) CaO(s) + CO2(g)

Reacting quicklime with water

• Calcium oxide (quicklime) is a base• It reacts with water to form calcium hydroxide

Ca(OH)2

• Calcium hydroxide is also known as slaked lime

Equation for this reaction

calcium + water calcium oxide hydroxide

CaO(s) + H2O(l) Ca(OH)2(aq)

Uses for slaked lime• 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

Another use for calcium hydroxide

• Calcium hydroxide is also called limewater• Limewater is used to test for the presence of

carbon dioxide gas• Clear lime water (calcium hydroxide

solution) turns white when carbon dioxide gas is passed through it.

Equation for this reaction

calcium + carbon calcium + waterhydroxide dioxide carbonate

Ca(OH)2(aq) + CO2(g) CaCO3(s) + H2O(l)

(clear) (white ppt)

The Limestone Cycle

These reactions all make up the limestone cycle.

limestone

Slaked lime

quicklimelimewater

heat

watermorewater

carbon dioxide

The limestone cycle

THE END

CaCO3

CaO

Ca(OH)2

Ca(OH)2