Limestone
Limestone is a type of sedimentary rock
that is mainly made up of a substance
called calcium carbonate.
Calcium carbonate has the chemical formula,
CaCO3
Because it has many uses and can be
used to make other products, limestone is
a valuable resource.
Basic properties of limestone
The appearance of limestone
can vary tremendously.
Limestone is calcium carbonate and like any carbonate,
it reacts with acids producing carbon dioxide gas.
Carbon dioxide turns limewater milky.
bubbles
of CO2
Because it reacts with
acids, it is sometimes
added to lakes to
remove acidity caused
by acid rain.
Limestone, chalk and marble are all forms of calcium
carbonate CaCO3.
Limestone
Chalk
Marble
Limestone is a sedimentary rock and most of it
(especially chalk) was formed from the remains of tiny
sea creatures.
This process took millions of years.
Limestone and chalk often contain fossils.
Where is
limestone
found in
the British
Isles?
limestone areas
There are
also limestone
cliffs on the
coast in the
Vale of
Glamorgan
Sedimentary rocks at Llantwit Major
in the Vale of Glamorgan
Layers of
limestone
and shale
fossils from rocks on left
fossils in the fallen limestone
blocks
prepared specimen – a Jurassic
oyster (180 million years old!)
More fossils found in limestone.
A Jurassic ammonite from
North Yorkshire.
180 million years old.
A Silurian gastropod (snail)
from Shropshire.
400 million years old.
Important uses of limestone
1. As a building material
Limestone has been used for thousands
of years for buildings and roads.
However, since it is attacked by acids
it is easily weathered and eroded.
2.
For making glass
Glass is made by heating a mixture of
limestone , sand and sodium carbonate (soda).
3. For making cement
Cement is made by heating together powdered limestone and clay
in a rotary kiln.
Limestone
and clay
Rotating
kiln
Gas
burners
Cement
Crusher
Cement
Mix with sand
and water and
chippings
concrete for
buildings etc.
Mix with sand
and water
mortar for joining
bricks together
Summary – the uses of limestone
Buildings
and roads
Mortar
(cement + water + sand)
Cement
(heat with clay)
Glass
(heat with sand
and sodium
carbonate)
CaCO3
Neutralise acidic soils
and lakes
Concrete
(cement + sand
+ gravel + water)
Limestone Quarrying
The quarrying of
limestone can have
major effects on the
environment.
Limestone quarrying provides the raw materials for making many
important substances such as glass and cement etc. It also
provides employment for people and benefits the local economy.
But what exactly are the
disadvantages?
Limestone Quarrying
– some disadvantages
An ‘eyesore’ in areas
of the countryside
Noise from
blasting
Loss of
habitat for
wildlife
Dust etc.
from lorries
Heating limestone
When limestone is strongly heated is
begins to glow (limelight!)
The thermal decomposition
of limestone
It decomposes to form calcium oxide
(quicklime) and carbon dioxide gas.
We can write a word equation:
calcium carbonate
calcium oxide
+
carbon dioxide
or a symbol equation:
CaCO3
CaO
+
CO2
This type of reaction, where a substance is broken down by heat is
called a THERMAL DECOMPOSITION
Calcium oxide (quicklime) is produced industrially using a lime kiln
Kiln rotates to ensure that the
limestone is mixed with the hot air
Air + carbon dioxide
Hot air
in
Limestone
in
Lime out
heat
calcium carbonate
calcium oxide + carbon dioxide
A thermal decomposition reaction
a lime kiln
Adding water to quicklime
‘slaking’ lime
When water is added to quicklime
(calcium oxide), the reaction produces
much heat and slaked lime (calcium
hydroxide) is formed.
A reaction that produces heat is called
an exothermic reaction.
We can write a word equation:
calcium oxide
+
water
calcium hydroxide
or in symbols
CaO
+
H 2O
Ca(OH)2
Calcium hydroxide solution is limewater which turns ‘milky’ with carbon dioxide.
Slaked lime (calcium hydroxide) also has uses:
 to neutralise acidic soil
 to make lime mortar
(often used to restore
old buildings
Heating other carbonates
A number of other carbonates are
decomposed in the same way as
calcium carbonate when heated e.g.
CuCO3
heat
copper carbonate
CuO + CO2
copper oxide + carbon dioxide
(green)
(black)
heat
zinc carbonate
zinc oxide + carbon dioxide
(Zinc oxide is yellow when hot, white
when cool)
ZnCO3
Both these reactions are again
examples of a thermal decomposition.
ZnO + CO2