Revision for IGCSE Sciences

1. INDUSTRIAL CHEMISTRYINDUSTRIAL CHEMISTRY
THE HABER PROCESS
This the process used to produce ammonia from nitrogen and
hydrogen gases.
N2(g) + 3H2(g)  2NH3
The reaction is reversible which means some of the products
turn back to reactants as soon as they are made, this means it
takes a long time to make an economical amount of ammonia.
To speed it up, the reaction is done:
• at high temperature (~450O
C)
• high pressure (~200 times atmospheric pressure)
• with a catalyst (iron oxide).
THE CONTACT PROCESS
This the process used to produce sulphuric acid and involves
three chemical reactions.
First sulphur is burnt in air to produce sulphur dioxide:
S (s) + O2 (g)  SO2 (g)
Secondly sulphur dioxide is reacted with further oxygen to make
sulphur trioxide:
2SO2 (g) + O2 (g)  SO3 (g)
This is reversible, so to maximise the amount of SO3:
• a high temperature (425O
C)
• medium-high pressure (1-2 times atmospheric pressure)
• a catalyst (vanadium (V) oxide, V2O5).
Finally, the sulphur trioxide is produced by first dissolving it in
sulphuric acid to make oleum (H2S2O7) which then makes more
sulphuric acid on the addition of water:
SO3 (g) + H2SO4 (l)  oleum
oleum + H2O (l)  2H2SO4 (l)
Note: trying to dissolve SO3 directly in water produces a very
dangerous mist of sulphuric acid.
Production of LIME
Lime is calcium oxide (CaO - ‘quicklime’) or calcium hydroxide (Ca(OH)2 - ‘slaked lime’)
Calcium oxide is made by the thermal decomposition of limestone (calcium carbonate) – heating it to
about 1000O
C:
CaCO3(s)  CaO(s) + CO2(g)
USE of quick lime:
Calcium oxide is one of the key ingredients in cement.
Calcium hydroxide is made by adding water to calcium oxide:
CaO + H2 O  Ca(OH)2
USES of slaked lime:
• Neutralising acidity in soils and lakes
• Neutralising acidity in industrial waste
• Sewage treatment – it helps small particles of waste to clump together so easily removed.
CRACKING of long alkanes
Because there is a greater need for hydrocarbons with shorter carbon chains we sometimes need to
cut longer chains into shorter ones using the process of cracking.
A long alkane is heated, vaporised and passed over a ceramic catalyst to produce a shorter alkane
and an alkene. Two examples:
C8H18  C4H10 + C4H8
C10H22  C7H16 + C3H6
POLYMERISATION to make macromolecules
Macromolecules are large molecules made from lots of smaller molecules – called monomers - joined
together. Macromolecules made of only one type of monomer are called polymers.
Addition Polymers – eg polythene, polystyrene, polyvinylchloride (PVC)
These are formed by monomers containing a C=C double bond. The double bonds link together to
form a continuous chain.
Condensation Polymers – e.g. nylon, polyester, Kevlar
In condensation polymerisation, each time two monomers join, one molecule of water is produced. In
the case of nylon (pictured) there are two
monomers – one with two acid ends (-COOH, black)
and one with two amine ends (-NH2, white).
They join with an ‘amide’ linkage, producing water.

2. EXTRACTION of Iron from Iron Ore using the BLAST FURNACE
Iron can be extracted from iron ore (Fe2O3, iron (III) oxide) and lead can be extracted from an ore
called galena (PbS, lead sulphide).
Metals that are less reactive than carbon can be extracted by using carbon as a reducing agent (to
steal the oxygen/sulphur). Metals that are more reactive than carbon must be produced by
electrolysis.
Iron is less reactive than carbon so can be reduced by it. This is done in a blast furnace. Study the
diagram then read the following:
Step 1: Carbon (coke) reacts with
oxygen (from the hot air blast):
C (s)+ O2(g)  CO2(g)
Step 2: Carbon dioxide reacts
with more carbon to make
carbon monoxide:
CO2(g) + C(s)  2CO(g)
Step 3: Carbon monoxide reduces
the iron oxide (iron ore) to make
molten liquid iron:
Fe2O3(s) + CO(g)  Fe(l) + CO2(g)
Step 1 happens here
Step 2 happens here
Step 3 happens here
PURIFICATION of Copper
When copper is made it contains lots of impurities. The copper is
purified by electrolysis. A large lump of impure copper is used as
the anode, the electrolyte is copper sulphate solution and the
cathode is made of pure copper.
At the anode, instead of anions losing electrons, neutral copper
atoms lose electrons to become copper ions .
Cu(s)  Cu2+
(aq) + 2e-
These then move through the electrolyte to the cathode where
they become copper atoms again.
Cu2+
(aq) + 2e-
 Cu(s)
The anode loses mass as copper atoms leave it and the cathode
gains mass as copper atoms join it. The impurities sink to the
bottom as a pile of sludge.
EXTRACTION of Aluminium from Bauxite by ELECTROLYSIS
Aluminium ore is called bauxite. Impurities are removed to leave aluminium oxide (Al2O3). The
aluminium oxide is dissolved in molten cryolite (as it has a lower melting point than aluminium
oxide by itself). This is poured into a large carbon lined vessel which acts as the cathode for
electrolysis.
A large anode made of carbon is lowered into the electrolyte. The processes that take place are:
At the cathode: aluminium ions gain electrons to make liquid aluminium
Al3+
+ 3e-
 Al(l)
At the anode: Oxide ions lose electrons to make oxygen gas
2O2-
 O2(g) + 2e-
The oxygen reacts with the carbon anode to make carbon dioxide, so the anodes have to be