✅ C617-618, extracting iron + aluminium Flashcards
How is iron extracted from its ore - what machinery
Using a large reaction container called a blast furnace
3 raw materials added to the top of the blast furnace - why
- iron ore, such as haematite, which contains iron(III) oxide
- coke
- limestone, which is used to purify the iron
What is coke - hows it made
Coke, is mostly carbon,
- is made by heating coal in the absence of air
What’s forced in at the bottom of the blast furnace
Hot air
REACTIONS IN A BLAST FURNACE - (1)
- what is formed - to be the main reducing agent in the blast furnace, and how it formed, brief
- Carbon can reduce iron(III) oxide to iron, but carbon monoxide is the main reducing agent in the blast furnace
- carbon monoxide is formed when coke reacts with carbon dioxide
3 stages to which iron(III) oxide is reduced in blast furnace
- involving prior to reduction what happens
- with symbol equations + state symbols
1 - Coke burns in the hot air, making carbon dioxide
C(s) + O2 —> CO2(g)
2 - More coke reduces the carbon dioxide, making carbon monoxide:
C(s) + CO2(g) —> 2CO(g)
3 - Carbon monoxide reduced iron(III) oxide to iron at around 1500C:
3CO(g) + Fe2O3(s) —> 3CO2(g) + 2Fe(l)
Once carbon monoxide has reduced iron(III) oxide to iron, what next? - in English words
- the molten iron trickles downwards in the blast furnace
- it contains sandy impurities from the iron ore
- these are removed using the limestone, which is mostly calcium carbonate
HOW are sandy impurities removed from the molten iron then
- 2 stages
- with symbol equations + state symbols
1 - Calcium carbonate (limestone) decomposes in the high temperatures:
CaCO3(s) —> CaO(s) + CO2(g)
2 - The calcium oxide formed reacts with silica from the sandy impurities to form calcium silicate.
CaO(s) + SiO2(g) —> CaSiO3(l)
WHAT is formed when the calcium oxide reacts with silica from the sandy impurities - and what happens then
Molten calcium silicate - called slag
It floats on the molten iron, and both the iron and slag are removed separately at the bottom of the blast furnace
SEE FIG 2 PAGE 208
4 uses of aluminium - not necessarily needed to know
Aircraft, overhead electricity cables, cooking foil, drinks cans
Aluminium
- how it exists
Aluminium exists naturally, mainly as Aluminium oxide, Al2O3, found in an ore called bauxite
Aluminium
- reactivity vs carbon
+ so… w/ problem
Aluminium is more reactive than carbon
- this means that, unlike iron and copper, it must be extracted from its ore by electrolysis
Problem:
- electrolysis only works if the compound is in solution or if it is molten — but aluminium oxide does not dissolve in water and its melting point is very high
Melting point of aluminium oxide
- Al2O3 - mp = over 2000C - so very difficult to heat aluminium oxide to this temperature
SOLUTION to how aluminium oxide is electrolysed
- melting point too high - prev card
- to get around this problem, aluminium oxide is dissolved in molten cryolite
- cryolite has a much lower melting point than aluminium oxide, and allows electrolysis to happen at about 950C
Aluminium oxide solubility in water?
Aluminium oxide is insoluble in water
Electrolysis process of aluminium
Cathode?
- the molten mixture of aluminium oxide and cryolite is contained in a huge electrolysis cell - made from steel, lined with graphite
- the graphite lining acts as the cathode, the negative electrode
Electrolysis process of aluminium
Anode?
- a series of large graphite blocks act as the anodes , the positive electrodes
What happens at cathode + anode during electrolysis of aluminium oxide
(3)
- aluminium is produced at the cathode
- oxygen is produced at the anode
The oxygen reacts with the hot graphite anodes, making carbon dioxide
Electrode reactions that happen during electrolysis of aluminium - half equations
At cathode:
Al3+ + 3e- —> Al
At anode:
2O2- —> O2 + 4e-
Even though aluminium is more abundant than iron in the Earth’s crust, aluminium is more expensive than iron.
Why?
This is mainly because of the large amounts of electrical energy used in the extraction process.
Why must aluminium be extracted using electrolysis?
Aluminium is more reactive than carbon so it must be extracted from its compounds using electrolysis.
ALUMINIUM ELECTROSLSI
The oxygen reacts with the carbon __, forming __ dioxide. So the __ gradually burn away. They must be __ frequently, adding to the __ of producing aluminium.
The oxygen reacts with the carbon anodes, forming carbon dioxide. So the anodes gradually burn away. They must be replaced frequently, adding to the cost of producing aluminium.
Overall reactions in a blast furnace - pb
