Transcript Limestone and its uses

The limestone cycle
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
Carbonate
CaCO3
heat
calcium
oxide
CaO
carbon
dioxide
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
Uses for quicklime
• Making cement,
mortar and
concrete.
• Decomposing rotting
bodies in mass graves
and reducing the
smell !
Making Slaked Lime
calcium + water
oxide
CaO
+
H 2O
calcium
hydroxide
Ca(OH)2
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
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
hydroxide dioxide
calcium + water
carbonate
Ca(OH)2 + CO2
CaCO3 +
H 2O
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
carbon
dioxide
limestone
heat
quicklime
limewater
more
water
water
Slaked lime