CALCIUM CARBONATE
Calcium carbonate (CaCO3) is an important raw material which occurs naturally as the
sedimentary rocks, limestone and chalk, and as the metamorphic rock, marble. These
rocks are obtained by quarrying.
Malham cove (limestone)
Dover cliffs (chalk)
marble quarry
Thermal Decomposition
When some substances are heated, they decompose (break down) into simpler
substances. This process is called THERMAL DECOMPOSITION. Calcium carbonate
undergoes thermal decomposition when heated in a kiln to about 1100 oC, forming
calcium oxide (quicklime) and carbon dioxide.
Other metal carbonates decompose in a similar way. The lower the metal is in the
reactivity series, the lower the temperature at which this decomposition takes place.
CaCO3(s)
CaO(s) + CO2(g)
Metal carbonates such as zinc and copper carbonates therefore decompose easily
whilst sodium and potassium carbonates do not. Sometimes we can tell that thermal
decomposition has occurred by a colour change (eg green copper carbonate turns
black).
CuCO3(s)
CuO(s) + CO2(g)
However if there is no colour change we can test for the production of CO2 gas using
limewater. If CO2 is given off the limewater will turn cloudy and decomposition has
occurred.
Test for CO2
When CO2 reacts with limewater the following reaction occurs which produces a white
insoluble precipitate (which makes it cloudy)
Ca(OH)2 (aq) +
CO2 (g)
Calcium hydroxide + carbon dioxide
(limewater)
TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 1
CaCO3(s)
+
H2O (l)
Calcium carbonate + water
Hydration
Quicklime reacts with water in a very exothermic reaction, forming calcium hydroxide
(slaked lime).
CaO(s) + H2O(l)
Ca(OH)2(s)
The Limestone Cycle
H2O
LIMESTONE
(calcium carbonate)
CO2
CO2
QUICKLIME
(calcium oxide)
SLAKED LIME
(calcium hydroxide)
H2O
Uses of Calcium Carbonate & Calcium Hydroxide
Building Material
Limestone is used as a building material. A form of limestone, called Portland stone,
was used in the construction of St Paul’s Cathedral in London. Limestone is a hard rock,
but it erodes badly in polluted urban environments, because it dissolves readily in acids.
Marble is used in sculpture and as a building material.
St. Paul’s Cathedral
TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 2
marble bust
Removal of Acidity
Powdered limestone is used to neutralise acidity in lakes and in light, sandy soils.
Slaked lime (calcium hydroxide) is used to neutralise acidity in heavy soils and in
drinking water.
Glass Manufacture
Glass is made by heating a mixture of:
 limestone
 sand
 sodium carbonate
Iron production
Limestone is added to the Blast Furnace, in the production of iron, to remove acidic
impurities present in iron ore.
Cement Manufacture
Cement is made by roasting
 powdered limestone with
 powdered clay
in a rotary kiln.
Mortar which is used to build a modern house today is a mixture of cement, sand and
water.
The hard, stone-like building material, concrete is made by mixing:
 cement
 water
 sand
 crushed rock
The soft mixture undergoes a slow chemical reaction and eventually sets hard.
TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 3


NEUTRALISATION


GLASS
heavy soils
drinking water
SLAKED
LIME
lakes
light soils
add water
QUICKLIME
heat + sand &
sodium carbonate
heat
LIMESTONE
CHALK
MARBLE
CALCIUM
CARBONATE
heat + powdered clay
BUILDING
removal of impurities
IRON & STEEL
TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 4
CEMENT
CONCRETE
mix with
 water
 sand
 crushed rock
END-OF-TOPIC TEST
1. Complete the following sentence by filling in the gaps.
The early atmosphere of the Earth consisted mainly of ........................................., like
the
present-day atmosphere
on
the planet
...............................................
This
atmosphere was formed by .....................................................................................
2. When plants evolved, the atmosphere on Earth began to change. Describe the
changes which took place and explain how they enabled life to establish itself on land.
.............................................................................................................................………….
..............................................................................................................................…………
..............................................................................................................................………...
.............................................................................................................................………....
3. The carbon cycle keeps the amount of carbon dioxide in the atmosphere almost
constant. State THREE ways in which carbon dioxide is released into the atmosphere.
.................................................................................................................…………..
.................................................................................................................……….....
.................................................................................................................……….....
State THREE ways in which carbon dioxide is removed from the atmosphere.
....................................................................................................................………..
....................................................................................................................………..
....................................................................................................................………...
4. Which gas is the main component of the Earth’s present-day atmosphere? How was
this gas formed?
..............................................................................................................................………...
..............................................................................................................................………...
TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 5
5. Give the names of two naturally occurring forms of calcium carbonate, one a
sedimentary rock, the other a metamorphic rock.
Sedimentary ........................................................................................................………....
Metamorphic ........................................................................................................………...
Complete this sentence:
When calcium carbonate is heated strongly, it undergoes a
chemical reaction called .......................................................................... and forms a gas
called ............................................................ and a solid called ......……...........................
This solid is also known as ...........................................................................
Describe what you would see when water is added to this solid.
..............................................................................................................................………...
6. How is calcium carbonate turned into cement?
..............................................................................................................................………....
Which other substances are added to cement to make concrete?
..............................................................................................................................………...
State THREE uses for calcium carbonate, other than in cement-making.
............................................................................................................................…..
.............................................................................................................................….
..............................................................................................................................…
7. What is the main reason for the rise in the average global temperature?
..............................................................................................................................………...
Describe the effect that this rise could have in Greenland and in Holland.
Greenland ............................................................................................................………....
.Holland ................................................................................................................………...
Describe one way in which we could attempt to reverse this change in climate.
..........................................................................................................................……….......
...............................................................................................................................………………….
TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 6