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Explainthe electro metallurgy of aluminium |
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Answer» SOLUTION :(i) In the methodHall- Heroldprocess,electrolysis is carriedout in an irontanklinedwith carbonwhichactsas a anode. (ii) The carbon blocksimmersed in theelectrolyteactsas a anode. (iii) A20 %solution of alumina,obtained fromthe bauxiteore is mixed withmolten Cryoliteand is takenin the electrolysis chamber. (iv) About10% calciumchlorideis alsoaddedto the solution . Caclium chloride HELPS to lowerthe melting point of the mixture. (v) THe fused mixtureis MAINTAINED at a temperature of abouve 1270 K (iv) The chemiacal reactionsinvolved in this processare Ionisation of alumina ` Al_(2) O_(3) to 2Al^(3+) + 3O^(2-)` Reaction of cathode ` 2Al^(3+)( " melt") + 6e^(-) to 2Al_(l)` Reaction at anode `6O^(2-) (" melt") to 3O_(2) + 12e^(-)` (vii)Sincecarbonactsas anodethe followingreaction takes place. ` C_(s) + O^(2-) "( melt") to CO + 2e^(-)` ` C_(s) + 2O^(2-) (" melt") to CO_(2) + 4e^(-)` (viii)Due to the abovetworeactions , anodesare slowlyconsumedduringthe electolysis , Thepurealuminiumis formedat thecathodeand settles at thebottom. (ix)The netelectrolysiscan be writtenas follows . `4Al^(3+) (" melt") + 6O^(2-) "( melt") + 3C_(s) to 4Al_(i) + 3CO_(2(g))` |
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