Saved Bookmarks
| 1. |
Explainthe electrometallurgyof aluminium. |
|
Answer» Solution :(i) In the method Hall- HeroIdprocess,electrolysis is carriedout in an irontanklinedwith carbonwhichactsas a cathode. (ii) The carbonblocksimmersed in the electrolyteactsas a anode. (iii) A 20%solution of alumina, obtained fromthe buxiteore is mixedwith molten Cryolite and is taken in theelectrolysischamber. (iv) About10%calcium chlorideis also addedto the solution . Calciumchloridehelps to lower the meltingpoint of the mixture. (v) The fusedmixture is maintained at a temperature of above1270 K. (vi) The chemicalreactionsinvolvedd in this process are Ionisation of alumina. ` Al_(2)O_(3) to2AI^(3+) + 3O^(2-)` Reaction at cathode ` 2AI^(3+) (" melt") + 6e^(-) to 2AI^(l)` Reaction at anode ` 6O^(2-) (" melt") to 3O_(2) + 12^(e-)` (vii) Sincecarbon acts as anode the followingreaction takesplace. `C_(s) + O^(2-) (" melt") to CO + 2e^(-) ` ` C_(s) + 2O^(2-) (" melt") to CO_(2) + 4e^(-)` (VIII) Due to the abovetwo reactions, anodes are slowly consumedduringthe electrolysis, The purealuminium is formed at thecathodand SETTLES at the BOTTOM. (IX) The net electrolysisreaction can be writtenas follows. ` 4AI^(3+) (" melt") + 6O^(2-) (" melt") + 3C_(s) to 4AI_(l) + 3CO_(2(g))` |
|