Extraction and uses of metals

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C4.01 Oxidation and reduction
Oxidation is a reaction where oxygen is gained. eg  iron + oxygen ---> iron oxide
Reduction is a reaction where oxygen is lost. Eg iron oxide is reduced to form iron.
Task C4.01 Classify the following reactions as oxidation or reduction: burning magnesium, making aluminium from aluminium oxide, burning carbon in air,
copper oxide + carbon --> copper + carbon dioxide
carbon monoxide forming carbon dioxide.

C4.02 Electron loss and gain
Oxidation is also a loss of electrons eg Fe --> Fe²⁺ + 2e^- 
Reduction also the gain of electrons eg (when Fe ions becomes Fe atoms)
Task C4.02 Identify all of the elements below as being oxidised or reduced in the following reactions: 
Cu²⁺ + 2e^- ---> Cu 
lead ions forming lead atoms
Na ---> Na⁺ + e^-
Ca + Cl₂ --> CaCl₂
Fe²⁺ ---> Fe³⁺ + e^-

C4.03 Reduction of metal ores
An ore is a material found in the ground which contains a metal.  An ore is often a metal oxide mixed with rock .  When a metal is extracted its ore is reduced.    Metal loses oxygen from its oxide.

See illustrations:  Examples include:  
haematite which is mostly iron III oxide Fe₂O₃
bauxite which is mostly aluminium oxide Al₂O₃
malachite which is mostly copper carbonate CuCO₃

C4.04 Extraction and position in reactivity series
The method of extraction of a metal depends on the reactivity of the metal.  
Unreactive metals like silver can be found uncombined. 
More reactive metals like iron can be reduced with carbon because carbon is more reactive than iron. 
Very reactive metals like aluminium can only be extracted by electrolysis. Carbon is not used as it is less reactive than aluminium.
Task C4.04

C4.05 The cost of electricity for extracting metals
Electrolysis is an extraction method that uses a lot of electrical energy. Electrical energy is more expensive than energy from burning carbon.
Task C4.05

C4.06 The extraction of aluminium
Aluminium is found in the ground in an ore called bauxite.  Bauxite is aluminium oxide  (Al₂O₃) with iron oxide impurities. After purification aluminium oxide is mixed with cryolite to lower the melting point from 2000º to 1000º, which saves money. This mixture is heated and the molten liquid used as the electrolyte. Both electrodes are made of graphite (carbon).  The anode (+ve) is graphite and the cathode (-ve) is a graphite lining to a steel case. The carbon anodes react with oxygen so have to be replaced.
C + O₂ --> CO₂

At cathode - positive aluminium ions attracted, gain electrons and become atoms.
Al³⁺ + 3e^- ---> Al

At anode - negative oxide ions attracted, lose electrons and become atoms.
2O^2- ----> O₂ + 4e^-

C4.07 Uses and properties of aluminium

Task C4.07

C4.08 Carbon and carbon monoxide for reducing oxides
Carbon and carbon monoxide can both remove oxygen from other compounds so are good for reduction.  They are used to reduce the ores of metals below carbon in the reactivity series.  E.g. zinc, iron, tin and lead.

C4.09 Iron extraction using the blast furnace

A blast furnace is used in the process of extracting iron. The raw materials iron ore, coke and limestone are put in at the top.  Hot air is blasted into this furnace at the bottom making the coke (carbon) burn faster and the temperature rises to about 1500º. When the coke burns, carbon dioxide is produced.
C + O₂ ---> CO₂
CO₂ reacts with the unburnt coke to form carbon monoxide CO
CO₂ + C ---> 2CO
Iron oxide Fe₂O₃  in the ore is reduced to iron by the reaction with the carbon monoxide.
3CO + Fe₂O₃ ---> 3CO₂ + 2Fe
Molten iron is a dense liquid, so runs to the bottom of the furnace and is tapped off.
Limestone CaCO₃ helps remove impurities during the extraction by forming calcium oxide CaO.
CaCO₃ ---> CaO + CO₂
The rock impurities silicon dioxide SiO₂ are then removed by the following reaction.
CaO + SiO₂ ---> CaSiO₃
CaSiO₃ is known as slag and can be used in making cement and road building.
Task C4.9

C4.10 The purification of copper

 
Task C4.10