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Sunday, August 14, 2011

Chemistry X-Extracting Metals towards the Top of the Activity Series

Extracting metals towards the top of activity series
The metals high up in the activity series are very reactive. They cannot obtain by reduction of their oxides by carbon.For example, carbon cannot reduce the oxides of sodium, magnesium, calcium, aluminium, etc., to the respective metals. This is because these metals have more affinity for oxygen than carbon. These metals are obtained by the electrolysis of their molten chlorides e.g. Extraction of Na from NaCl
At cathode Na+ + e---à Na
At anode 2Cl-       ----à  Cl2 + 2e-
Similarly, aluminium is obtained by the electrolytic reduction of aluminium oxide.
    Metal                           Method of reduction of oxide
K     Na          Ca           All these metals cannot be reduced by coke or carbon monoxide.
Mg   Al                         Electrolytic method is the only way to reduce these metals
Reduction by Electrolysis
This process is used for oxides of highly reactive metals that are above aluminium in the reactivity series. It is also used for reduction of aluminium oxide. Example:
2Al2O3 ---------electricity-----> 4 Al + 3 O2
Reduction Using Aluminium (Aluminothermy)
Aluminium is an expensive reducing agent. It is used for reduction of oxides of highly reactive metals. But these metals need to be below aluminium in the reactivity series. Example:
Cr2O3 + 2Al ----Heat------->   Al2O3 + 2Cr
Aluminothermy is also used for welding broken iron rails.
Fe2O3 + 2Al ---Heat----->      2Fe + Al2O3

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