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How is the extraction of aluminium?
The ore of aluminium is bauxite (Al2O3.2H2O).Purification of bauxite is done by leaching with NaOH .Aluminium oxide disolves in NaOH forming soluble sodiumaluminate(NaAlO2).It is filtered and to the filtrate added Al(OH)3 to get the precipitate of it .Al(OH)3 is heated to get Al2O3 ,alumina.This process is called leaching .
   Al2O3 +2NaOH ________>2NaAlO2  + H2O
   NaAlO2  +2H2O_________>Al(OH)3 +NaOH
   2Al(OH)3   at 1200 oc  __________>Al2O3   +3H2O
  
 Electrolysis of alumina 
 Alumina is dissolved in molten cryollite and is electrolysed in an iron tank lined with carbon act as the cathode .Carbon rods dipped in it act as the anode .When electricity is passed through it , the following reaction will takes place .
  2Al(OH)3   (at 1200 oc ) __________>  Al2O3  + 3n2O
                          Al  3+   +3e-    __________>  Al(cathode )
                      2O2- +C  __________>  CO2 +ve (anode)
Aluminium obtained is further refined by electrolysis .


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