GCSE CHEMISTRY
NOTES
These notes contain:
C 1.2.1 – CALCIUM CARBONATE
C1 LIMESTONE NOTES BY MISS CHOHAN
C 1.2 - LIMESTONE
The chemical name and formula of Limestone is Calcium carbonate (CaCO3)
Limestone was formed when CO2 from the air became `locked` in the shells of sea creatures
Limestone is a sedimentary rock. This type of rock will have shells from sea creatures which
become fossilised inside the rock
Calcium carbonate is made up of 3 elements:
 Calcium
 Carbon
 Oxygen
CaCO3 contains:
1 atom of calcium
1 atom of carbon
3 atoms of oxygen
5 atoms in total
Limestone is very important for farmers which uses products made from limestone to neutralise
acid soil
Limestone is also important in making building materials such as cement, mortar and concreate.
Limestone buildings can react with acid rain ∴ corroding it over a period of time
Thermal decomposition is when high temperatures are used to break down a compound into
two or more substances
Limestone thermally decomposes to form calcium oxide and carbon dioxide as follows:
Calcium carbonate  Calcium oxide + Carbon dioxide
CaCO3(s)  CaO(s) + CO2(g)
Calcium oxide is a white solid
Thermal decomposition is an ENDOTHERMIC process (i.e. heat energy is taken in)
C1 LIMESTONE NOTES BY MISS CHOHAN
Thermal decomposition occurs in a ROTARY KILN (i.e. a rotating oven)
All metal carbonates decompose thermally in the same way:
Sodium carbonate  Sodium oxide + Carbon dioxide
Na2CO3(s)  Na2O(s) + CO2(g)
Magnesium carbonate  Magnesium oxide + Carbon dioxide
MgCO3(s)  MgO(s) + CO2(g)
Zinc II carbonate  Zinc II oxide + carbon dioxide
ZnCO3(s)  ZnO(s) + CO2(g)
 The limestone is crushed to increase the surface area allowing thermal
decomposition to occur quicker
 Methane is used as a fuel in the rotary kiln to provide heat energy to thermally
decompose the limestone
 The two waste gases produced in the rotary kiln are:
i)
Carbon dioxide (formed from the thermal decomposition of limestone
ii)
and by the combustion of methane)
Nitrogen (since 78% of the atmosphere is nitrogen)
A rotating kiln is used to allow the limestone to mix with the stream of hot air therefore
allowing the limestone to decompose completely.
C1 LIMESTONE NOTES BY MISS CHOHAN
THERMAL DECOMPOSITION OF METAL CARBONATES & THE REACTIVITY SERIES
Metal carbonates such as calcium carbonate or copper carbonate break down when heated strongly.
When a compound splits into two or more by heat it is referred to as thermal decomposition.
e.g.
calcium carbonate  calcium oxide + carbon dioxide
CaCO3 (s)

CaO (s)
+
CO2 (s)
The rate at which a metal carbonates decompose can be investigated using the following apparatus.
The speed of decomposition can be measured by timing the colour change of limestone. It turns from
clear to milky in the presence of carbon dioxide
No reaction is observed with sodium carbonate as the more reactive metal makes the carbonate more
stable.
Calcium is less reactive than sodium therefore heat is able to decompose calcium carbonate fairly
easily.
calcium carbonate  calcium oxide + carbon dioxide
CaCO3

CaO
+
CO2
Copper is the least reactive metal and decomposes rapidly.
copper carbonate  copper oxide + carbon dioxide
CuCO3

CuO
+
CO2
The more reactive the metal the more stable the carbonate
C1 LIMESTONE NOTES BY MISS CHOHAN
WITH ACIDS
Limestone like all metal carbonates react with acids as follows:
METAL
+
ACID

SALT
CARBONATE
+
CARBON
+ WATER
DIOXIDE
Calcium carbonate + Hydrochloric acid  Calcium chloride + Carbon dioxide + Water
CaCO3(s) + 2HCl(aq)  CaCl2(aq) + CO2(g) + H2O(l)
Magnesium carbonate + Sulphuric acid  Magnesium sulphate + Carbon dioxide + Water
MgCO3(s) + H2SO4(aq)  MgSO4(aq) + CO2(g) + H2O(l)
 Bubble carbon dioxide gas through limewater
 The limewater goes cloudy/milky
NOTE: Limewater is also called calcium hydroxide solution Ca(OH)2(aq).
This solution is an alkalis since it contains hydroxide ions in it.
Carbon dioxide gas is acidic so when this gas is bubbled through limewater (or calcium
hydroxide solution), a neutralisation reaction takes place i.e.
Calcium hydroxide solution + Carbon dioxide  Calcium carbonate + Water
(Limewater)
Ca(OH)2(aq) + CO2(g)  CaCO3(s) + H2O(l)
It is the calcium carbonate which forms that causes the
cloudiness as its an insoluble white precipitate.
CALCIUM OXIDE
This is a white solid formed from the thermal decomposition of limestone (CaCO3):
CaCO3(s)  CaO(s) + CO2(g)
Calcium oxide is a base and farmers sprinkle it on their fields to neutralise the acid in the soil
(from acid rain)
C1 LIMESTONE NOTES BY MISS CHOHAN
CALCIUM HYDROXIDE
Calcium hydroxide solution (Ca(OH)2) is an alkalis. It is formed when calcium oxide reacts with
water i.e.
Calcium oxide + Water  Calcium hydroxide
CaO(s) + H2O(l)  Ca(OH)2 (aq)
This is a highly EXOTHERMIC reaction (heat energy is given out)
Calcium hydroxide solution is also used by farmers to neutralise acid soil.
THE LIMESTONE CYCLE
Bubble
through
STEP 1
CALCIUM CARBONATE
CO2
THERMAL
DECOMPOSITION
CO2
CALCIUM OXIDE
CALCIUM HYDROXIDE SOLUTION
STEP 2
Add a little water
STEP 3
Add excess water and
filter
CALCIUM
HYDROXIDE
C1 LIMESTONE NOTES BY MISS CHOHAN
Calcium carbonate (limestone) is heated for 20
minutes. Limestone glows and becomes crumbly.
This decomposes it to calcium oxide (quicklime)
A few drops of water are added to the calcium
oxide (quicklime). This causes the compound to
sizzle and release steam. This forms calcium
hydroxide (slaked lime). The reaction is
exothermic.
Calcium hydroxide (slaked lime) dissolves a
little in water. Excess water is added to
form an alkaline solution called limewater.
C1 LIMESTONE NOTES BY MISS CHOHAN
Carbon dioxide passed into limewater gives a milky solution, this is due to the insoluble
calcium carbonate formed
Clear limewater turning milky is the test for carbon dioxide gas
C1 LIMESTONE NOTES BY MISS CHOHAN
U
Limestone can be used to make:
 Cement
 Mortar (stuff you stick bricks with)
 Concrete
 & Glass
CEMENT
Is made by adding:
LIMESTONE + CLAY
Heat in a rotary kiln

CEMENT
MORTAR
Is made by mixing:
CALCIUM HYDROXIDE +CEMENT + SAND + WATER  MORTAR
Mortar has one major disadvantage as a building material and that is it takes time for it to
harden.
Mortar will only harden once the calcium hydroxide (alkalis) reacts with the carbon dioxide in
the air (acidic gas). This reaction produces calcium carbonate (CaCO3 OR LIMESTONE!)
which hardens over time
CONCRETE
Is made by mixing:
CEMENT + SAND + WATER + GRAVEL (OR AGGREGATE)  CONCRETE
NOTE: Gravel or aggregate are small stones
Concrete has many advantages as a building material:





Its strong
Resists forces like stretching, crushing, squashing
Can be poured into moulds
Can be reinforced using steel rods making them even stronger
Do not react with acid rain
C1 LIMESTONE NOTES BY MISS CHOHAN
ADVANTAGES
 Provides jobs
 Brings money into the area
 This leads to improvement in transport links, health facilities, more schools in the area and
encourages more businesses into the area so bringing more money into the area
 Once quarrying is complete the land is landscaped to provide leisure facilities and provide
jobs
DISADVANTAGES




Looks ugly (eyesore!)
Causes noise and dust pollution
Destroys habitats
Causes extra traffic
LIMESTONE VERSES CONCRETE VERSES STONE AS BUILDING MATERIALS
LIMESTONE
ADVANTAGES
Is soft ∴ can easiliy be cut
Is cheaper than most rocks e.g. marble
and granite
Limestone is abundant
Limestone is a natural rock ∴ does not




DISADVANTAGES

Limestone reacts with acid rain

Limestone is NOT fire resistant
need further processing
Has a nice appearance to make buildings

CONCRETE
ADVANTAGES


Can be reinforced with steel rods to
make them stronger
Can be poured into moulds
Cheap way to construct building

materials rather than use iron or steel
Does not react with acid rain

Is fire resistant

DISADVANTAGES

Concrete has low tensile strength ∴
can easily be cracked


Concrete buildings look ugly
The process of making concrete
involves burning fossil fuels ∴ CO2
forms which contributes to global
warming
C1 LIMESTONE NOTES BY MISS CHOHAN
STONE (LIKE SLATE)
ADVANTAGES

Hard

Strong



Abundant
Fire resistant
Does not corrode with acid rain
DISADVANTAGES



Looks ugly
Can’t be poured into moulds
Expensive
OTHER USES OF LIMESTONE




It is used in the production of steel and iron. It is added to iron ore and coke in the blast
furnace to remove impurities.
It is used as a road stone when mixed with bitumen as it has strong physical properties.
It is used to make cement when it is mixed with clay or sandstone. This can then be mixed
with aggregates (mixture of building rocks) to form concrete.
Limestone is used to neutralise and raise the pH of acidic soils (which are usually less than


pH 6.5).
Quicklime and slaked lime are added to acidic lakes to improve the diversity of aquatic life.
Limestone is used to absorb acidic waste gases like sulfur dioxide in power station
chimneys. These are referred to as ‘sulfur scrubbers’.
It is used to make glass
Used in the manufacture of medicinal antacids

It is used in toothpastes as abrasive


C1 LIMESTONE NOTES BY MISS CHOHAN