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Secondary 4 Chemistry Extraction of Aluminium via electrolysis JT 2009

Raffles Programme. Secondary 4 Chemistry Extraction of Aluminium via electrolysis JT 2009. Extraction of Aluminium. Bauxite is mined. Bauxite comprises: Al 2 O 3 - aluminium oxide Fe 2 O 3 - iron(III) oxide SiO 2 - silicon dioxide.

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Secondary 4 Chemistry Extraction of Aluminium via electrolysis JT 2009

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  1. Raffles Programme Secondary 4 Chemistry Extraction of Aluminium via electrolysis JT 2009

  2. Extraction of Aluminium Bauxite is mined Bauxite comprises:Al2O3 - aluminium oxideFe2O3 - iron(III) oxideSiO2 - silicon dioxide purified by treating with NaOH (Al2O3 is amphoteric and reacts with NaOH) Al2O3 - aluminium oxide (or alumina) High m.p. : 2045 oC Used as the electrolyte  aluminium Na3AlF6 , cryolite is added to lower the m.p. to 950 oC (this means a great cost reduction!) 2

  3. Electrolysis 1. anode: carbon oxidation occurs: 2O2- (l)  O2(g) + 4e- 2. cathode: carbon O2- reduction occurs: O2- O2- Al3+(l) + 3e- Al(l) Al3+ 3. electrolyte: Al2O3 dissolved in cryolite Al3+ 4. steel tank 5. molten aluminium is extracted Overall equation:4Al3+(l) + 6O2-(l)  4Al(l) + 3O2(g) - + 3 (play video)

  4. At the anode: anode reaction: 2O2- (l)  O2(g) + 4e- + - oxygen is produced - the oxygen reacts with the anode, which are at high temperatureto produce carbon dioxide - the anode has to be periodically replaced

  5. Uses of Aluminium construction of aircraft, lightweight vehicles, and ladders(alloy - duralumin* used for aircraft) cookware e.g. pots, pans, utensils window frames aluminium foil (play video) high tension electric cables(its low density is an advantage) * Duralumin: aluminium (94%), copper (4%) and magnesium (1%). 5

  6. Side questions 6

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