IGCSE
GENERAL PRINCIPLES
OCCURRENCE
• ores of some metals are very common (iron, aluminium)
• others occur only in limited quantities in selected areas
• high grade ores are cheaper to process because,
ores need to be purified before being reduced to the metal
GENERAL PRINCIPLES
THEORY
The method used to extract metals depends on the . . .
• purity required
• energy requirements
• cost of the reducing agent
• position of the metal in the reactivity series
GENERAL PRINCIPLES
REACTIVITY SERIES
K Na Ca Mg Al C Zn Fe H Cu Ag
• lists metals in descending reactivity
• hydrogen and carbon are often added
• the more reactive a metal the less likely it will be found in
its pure, or native, state
• consequently, it will be harder to convert it back to the metal.
GENERAL PRINCIPLES
METHODS - GENERAL
Low in series occur native or
Cu, Ag extracted by roasting an ore
Middle of series metals below carbon are extracted by reduction
Zn, Fe of the oxide with carbon or carbon monoxide
High in series reactive metals are extracted using electrolysis
Na, Al - an expensive method due to energy costs
Variations can occur due to special properties of the metal.
GENERAL PRINCIPLES
METHODS - SPECIFIC
• reduction of metal oxides with carbon IRON
• reduction of metal oxides by electrolysis ALUMINIUM
IRON
EXTRACTION OF IRON
GENERAL PROCESS
• occurs in the BLAST FURNACE
• high temperature process
• continuous
• iron ores are REDUCED by carbon / carbon monoxide
• is possible because iron is below carbon in the reactivity series
EXTRACTION OF IRON
RAW MATERIALS
THE BLAST FURNACE
G
IN THE BLAST
FURNACE IRON ORE
IS REDUCED TO IRON.
A
THE REACTION IS
POSSIBLE BECAUSE C
CARBON IS ABOVE IRON
IN THE REACTIVITY
SERIES D
Click on the letters to see B B
what is taking place
E
F
THE BLAST FURNACE
COKE, LIMESTONE
AND IRON ORE ARE Now move the
ADDED AT THE TOP
A cursor away
from the tower
THE BLAST FURNACE
HOT AIR IS BLOWN IN
NEAR THE BOTTOM
CARBON + OXYGEN CARBON + HEAT
DIOXIDE
C + O2 CO2
OXYGEN IN THE AIR
REACTS WITH CARBON IN
THE COKE. THE REACTION
IS HIGHLY EXOTHERMIC B B
AND GIVES OUT HEAT.
Now move the
cursor away
from the tower
THE BLAST FURNACE
THE CARBON DIOXIDE
PRODUCED REACTS
WITH MORE CARBON
TO PRODUCE Now move the
CARBON MONOXIDE C cursor away
from the tower
CARBON + CARBON CARBON
DIOXIDE MONOXIDE
C + CO2 2CO
THE BLAST FURNACE
THE CARBON
MONOXIDE REDUCES
THE IRON OXIDE
CARBON + IRON CARBON + IRON
MONOXIDE OXIDE DIOXIDE
Now move the
3CO + Fe2O3 3CO2 + 2Fe D cursor away
from the tower
REDUCTION INVOLVES
REMOVING OXYGEN
THE BLAST FURNACE
SILICA IN THE IRON
ORE IS REMOVED BY
REACTING WITH LIME
PRODUCED FROM
THE THERMAL
DECOMPOSITION OF
LIMESTONE
CaCO3 CaO + CO2
CaO + SiO2 CaSiO3
CALCIUM SILICATE (SLAG)
IS PRODUCED
E
MOLTEN SLAG IS RUN OFF Now move the
AND COOLED cursor away
from the tower
THE BLAST FURNACE
MOLTEN IRON RUNS
TO THE BOTTOM OF
THE FURNACE.
IT IS TAKEN OUT
(CAST) AT REGULAR
INTERVALS
CAST IRON
- cheap and easily moulded
- used for drainpipes, engine blocks
F Now move the
cursor away
from the tower
THE BLAST FURNACE
G
HOT WASTE GASES
ARE RECYCLED TO
AVOID POLLUTION
AND SAVE ENERGY
CARBON MONOXIDE - POISONOUS
SULPHUR DIOXIDE - ACIDIC RAIN
CARBON DIOXIDE - GREENHOUSE GAS
RECAP
SLAG PRODUCTION
• silica (sand) is found with the iron ore
• it is removed by reacting it with limestone
• calcium silicate (SLAG) is produced
• molten slag is run off and cooled
• it is used for building blocks and road foundations
SLAG PRODUCTION
• silica (sand) is found with the iron ore
• it is removed by reacting it with limestone
• calcium silicate (SLAG) is produced
• molten slag is run off and cooled
• it is used for building blocks and road foundations
EQUATIONS
limestone decomposes on heating CaCO3 —> CaO + CO2
calcium oxide combines with silica CaO + SiO2 —> CaSiO3
overall CaCO3 + SiO2 —> CaSiO3 + CO2
WASTE GASES AND POLLUTION
SULPHUR DIOXIDE
• sulphur is found in the coke; sulphides occur in the iron ore
• burning sulphur and sulphides S + O2 ——> SO2
produces sulphur dioxide
• sulphur dioxide gives SO2 + H2O ——> H2SO3
rise to acid rain sulphurous acid
CARBON DIOXIDE
• burning fossil fuels increases the amount of this greenhouse gas
LIMITATIONS OF CARBON REDUCTION
Theoretically, several other important metals can be extracted this
way but are not because they combine with the carbon to form a
carbide
e.g. Molybdenum, Titanium, Vanadium, Tungsten
STEEL MAKING
Iron produced in the blast furnace is very brittle due to the high
amount of carbon it contains.
In the Basic Oxygen Process, the excess carbon is burnt off in a
converter and the correct amount of carbon added to make steel.
Other metals (e.g. chromium) can be added to make specialist steels.
Removal of impurities
SILICA add calcium oxide CaO + SiO2 ——> CaSiO3
CARBON add oxygen C + O2 ——> CO2
PHOSPHORUS add oxygen 2P + 5O2 ——> P4O10
SULPHUR add magnesium Mg + S ——> MgS
TYPES OF STEEL
MILD easily pressed into shape chains and pylons
LOW CARBON soft, easily shaped
HIGH CARBON strong but brittle chisels, razor blades,
saws
STAINLESS hard, resistant to corrosion tools, sinks, cutlery
(contains chromium and nickel)
COBALT can take a sharp edge high speed cutting tools
can be magnetised permanent magnets
MANGANESE increased strength points in railway tracks
NICKEL resists heat and acids industrial plant, cutlery
TUNGSTEN stays hard at high temps high speed cutting tools
Click to watch the video
ALUMINIUM
EXTRACTION OF ALUMINIUM
EXTRACTION OF ALUMINIUM
RAW MATERIALS
BAUXITE aluminium ore
Bauxite contains alumina (Al2O3 aluminium oxide) plus
impurities such as iron oxide – it is purified before use.
EXTRACTION OF ALUMINIUM
RAW MATERIALS
BAUXITE aluminium ore
Bauxite contains alumina (Al2O3 aluminium oxide) plus
impurities such as iron oxide – it is purified before use.
CRYOLITE Aluminium oxide has a very
high melting point.
Adding cryolite lowers the
melting point and saves
energy.
EXTRACTION OF ALUMINIUM
ELECTROLYSIS
Unlike iron, aluminium cannot be extracted using carbon.
(Aluminium is above carbon in the reactivity series)
EXTRACTION OF ALUMINIUM
ELECTROLYSIS
Unlike iron, aluminium cannot be extracted using carbon.
(Aluminium is above carbon in the reactivity series)
Reactive metals are extracted using electrolysis
EXTRACTION OF ALUMINIUM
ELECTROLYSIS
Unlike iron, aluminium cannot be extracted using carbon.
(Aluminium is above carbon in the reactivity series)
Reactive metals are extracted using electrolysis
Electrolysis is expensive - it requires a lot of energy…
- ore must be molten (have high melting points)
- electricity is needed for the electrolysis process
EXTRACTION OF ALUMINIUM
ELECTROLYSIS
SOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITY
THIS IS BECAUSE THE IONS ARE NOT FREE TO MOVE
EXTRACTION OF ALUMINIUM
ELECTROLYSIS
SOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITY
THIS IS BECAUSE THE IONS ARE NOT FREE TO MOVE
DISSOLVING IN WATER or… MELTING
ALLOWS THE IONS TO MOVE FREELY
EXTRACTION OF ALUMINIUM
ELECTROLYSIS
SOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITY
THIS IS BECAUSE THE IONS ARE NOT FREE TO MOVE
DISSOLVING IN WATER or… MELTING
ALLOWS THE IONS TO MOVE FREELY
POSITIVE IONS MOVE TO THE NEGATIVE
ELECTRODE
NEGATIVE IONS MOVE TO THE POSITIVE
ELECTRODE
EXTRACTION OF ALUMINIUM
EXTRACTION OF ALUMINIUM
CARBON ANODE
THE CELL CONSISTS OF A CARBON ANODE
EXTRACTION OF ALUMINIUM
STEEL
CATHODE
CARBON
LINING
THE CELL CONSISTS OF A CARBON LINED
STEEL CATHODE
EXTRACTION OF ALUMINIUM
MOLTEN
ALUMINA and
CRYOLITE
ALUMINA IS DISSOLVED IN MOLTEN CRYOLITE Na3AlF6
SAVES ENERGY - the mixture melts at a lower temperature
EXTRACTION OF ALUMINIUM
MOLTEN
ALUMINA and
CRYOLITE
ALUMINA IS DISSOLVED IN MOLTEN CRYOLITE Na3AlF6
aluminium and oxide ions are now free to move
EXTRACTION OF ALUMINIUM
POSITIVE
ALUMINIUM IONS
ARE ATTRACTED
TO THE
NEGATIVE
CATHODE
CARBON CATHODE
Al3+ + 3e- Al
EACH ION PICKS UP 3 ELECTRONS AND IS DISCHARGED
EXTRACTION OF ALUMINIUM
NEGATIVE OXIDE
IONS ARE CARBON ANODE
ATTRACTED TO
THE POSITIVE
ANODE
O2- O + 2e-
EACH ION GIVES UP 2 ELECTRONS AND IS DISCHARGED
EXTRACTION OF ALUMINIUM
ELECTRONS
CARBON ANODE
CARBON CATHODE
EXTRACTION OF ALUMINIUM
ELECTRONS
OXIDATION (LOSS OF
ELECTRONS) TAKES PLACE
AT THE ANODE
CARBON ANODE
ANODE 3O2- 1½O2 + 6e- OXIDATION
EXTRACTION OF ALUMINIUM
ELECTRONS
OXIDATION (LOSS OF
ELECTRONS) TAKES PLACE
AT THE ANODE
REDUCTION (GAIN
OF ELECTRONS)
TAKES PLACE AT
THE CATHODE CARBON CATHODE
ANODE 3O2- 1½O2 + 6e- OXIDATION
CATHODE 2Al3+ + 6e- 2Al REDUCTION
EXTRACTION OF ALUMINIUM
ELECTRONS
OXIDATION (LOSS OF
ELECTRONS) TAKES PLACE
AT THE ANODE
CARBON ANODE
REDUCTION (GAIN
OF ELECTRONS)
TAKES PLACE AT
THE CATHODE CARBON CATHODE
ANODE 3O2- 1½O2 + 6e- OXIDATION
CATHODE 2Al3+ + 6e- 2Al REDUCTION
EXTRACTION OF ALUMINIUM
CARBON DIOXIDE
PROBLEM
THE CARBON
CARBON ANODE
ANODES REACT
WITH THE
OXYGEN TO
PRODUCE
CARBON DIOXIDE
EXTRACTION OF ALUMINIUM
CARBON DIOXIDE
PROBLEM
THE CARBON
CARBON ANODE
ANODES REACT
WITH THE
OXYGEN TO
PRODUCE
CARBON DIOXIDE
THE ANODES HAVE TO BE REPLACED AT
REGULAR INTERVALS, THUS ADDING TO THE
COST OF THE EXTRACTION PROCESS
PROPERTIES OF ALUMINIUM
ALUMINIUM IS NOT AS REACTIVE AS ITS POSITION
IN THE REACTIVITY SERIES SUGGESTS
THIS IS BECAUSE A THIN LAYER OF ALUMINIUM
OXIDE QUICKLY FORMS ON ITS SURFACE AND
PREVENTS FURTHER REACTION TAKING PLACE
THIN LAYER
OF OXIDE
ANODISING PUTS ON A CONTROLLED LAYER SO
THAT THE METAL CAN BE USED FOR HOUSEHOLD
ITEMS SUCH AS PANS AND ELECTRICAL GOODS
Click to watch the video
SODIUM
EXTRACTION OF SODIUM
Involves electrolysis of molten sodium chloride in the Down’s Cell.
CaCl2 is mixed with the sodium chloride to lower the melting point and
reduce energy costs.
Sodium is discharged at the cathode Na+ + e¯ ——> Na
Chlorine is discharged at the anode Cl¯ ——> ½Cl2 + e¯
RECYCLING
Problems • high cost of collection and sorting
• unsightly plant
• high energy process
Social • less visible pollution of environment by waste
benefits • provides employment
• reduces the amount of new mining required
Economic • maintains the use of valuable resources
benefits • strategic resources can be left underground
Purification of Copper
impure copper pure copper
anode cathode
54
Purification of Copper
Copper is easily extracted by r ________, but it
then needs to be purified by e_________.
The p_______ electrode is impure copper.
At this electrode copper ions (Cu2+) move into
the solution.
Copper ions are attracted to the n_______
electrode to form copper atoms.
Impurities fall to the bottom.
55
Click to watch the video
