The chemistry and uses of limestone

1. 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.

2. 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.
bubbles
of CO2
Carbon dioxide turns limewater milky.
Because it reacts with acids, it is
sometimes added to lakes to
remove acidity caused by acid rain.

3. Limestone is a sedimentary rock and most of it (especially chalk)
was formed from the remains of tiny sea creatures.
Limestone, chalk and marble are all forms of calcium carbonate
CaCO3.
Limestone Chalk Marble
This process took millions of years.
Limestone and chalk often contain fossils.

4. Where is limestone
found in the British
Isles?
limestone areas
There are also limestone
cliffs on the coast in the
Vale of Glamorgan

5. Sedimentary rocks at Llantwit Major
in the Vale of Glamorgan
Layers of
limestone
and shale
fossils in the fallen limestone
blocks
fossils from rocks on left
prepared specimen – a Jurassic
oyster (180 million years old!)

6. 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.

7. Important uses of limestone
As a building material1.
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.

8. 2. For making glass
Glass is made by heating a mixture of
limestone , sand and sodium carbonate (soda).

9. For making cement
Cement is made by heating together powdered limestone and clay
in a rotary kiln.
Limestone
and clay Rotating
kiln
Gas
burners
Crusher
Cement
3.

10. Cement
mortar for joining
bricks together
concrete for
buildings etc.
Mix with sand
and water
Mix with sand
and water and
chippings

11. Summary – the uses of limestone
Buildings
and roads
Glass
(heat with sand
and sodium
carbonate)
Neutralise acidic soils
and lakes
Cement
(heat with clay)
Mortar
(cement + water + sand)
Concrete
(cement + sand +
gravel + water)
CaCO3

12. Limestone Quarrying
The quarrying of
limestone can have
major effects on the
environment.

13. 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?

14. Limestone Quarrying
– some disadvantages
An ‘eyesore’ in areas
of the countryside
Noise from
blasting
Dust etc.
from lorries
Loss of
habitat for
wildlife

15. Heating limestone
When limestone is strongly heated
is begins to glow (limelight!)
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
The thermal decomposition
of limestone

16. Calcium oxide (quicklime) is produced industrially using a lime kiln
Limestone
in
Hot air
in
Kiln rotates to ensure that the
limestone is mixed with the hot air
Air + carbon dioxide
Lime out
calcium carbonate
heat
calcium oxide + carbon dioxide
A thermal decomposition reaction
a lime kiln

17. Adding water to quicklime
Calcium hydroxide solution is limewater which turns ‘milky’ with carbon dioxide.
We can write a word equation:
calcium oxide + water calcium hydroxide
CaO + H2O Ca(OH)2
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.
or in symbols
‘slaking’ lime

18. Slaked lime (calcium hydroxide) also has uses:
 to neutralise acidic soil
 to make lime mortar
(often used to restore
old buildings

19. Heating other carbonates
A number of other carbonates are
decomposed in the same way as
calcium carbonate when heated e.g.
copper carbonate copper oxide + carbon dioxide
zinc carbonate zinc oxide + carbon dioxide
Both these reactions are again
examples of a thermal decomposition.
heat
(green) (black)
CuCO3 CuO + CO2
(Zinc oxide is yellow when hot, white
when cool)
heat
ZnCO3 ZnO + CO2