Section 2: Aluminum In Chemistry As The Most Abundant Element In Earth’S Crust

SECTION 2 : ALUMINIUM IN CHEMISTRY AS THE MOST ABUNDANT ELEMENT IN EARTH’S CRUST Aluminum is the third most abundant element in the earth's crust (after oxygen and silicon), reaching 8.2% of the total mass.The most important ore for aluminum production is bauxite, which is hydrated aluminum oxide containing 50 – 60% Al2 O3 , 1 – 20% Fe2 O3 , 1 – 10% silica, a little transition metal, and the rest is water. Aluminum is obtained using the Hall-Heroult process, after the names of its discoverers Charles M. Hall (USA) and Paul Heroult (France) in 1886. This processing includes two stages. 1. Purification Stage At this stage, aluminum produced from bauxite which contains iron oxide (Fe 2O3) and silica is purified by dissolving the bauxite in NaOH(aq). Iron oxide (Fe 2O3) which is basic in nature does not dissolve in NaOH solution. Reaction: Al2O3 (s) + 2 NaOH(aq) 2NaAlO2 (aq) + H2O The above solution is then acidified to precipitate Al(OH)3 (s). Pure Al2O3 can be produced by heating Al(OH)3 , then filtering it to obtain Al2O3. Reaction: NaAlO2(aq) + HCl(aq) + H2O Al(OH)3 (s) + NaCl(aq) 2 Al(OH)3 (s) Al2O3 (s) + 3H2O(g) 2. Electrolysis Stage Al2 O3 (with a melting point of 2,030 °C) is mixed with cryolite (Na3 AlF6 ) (to lower the melting point to 1,000 °C). The Al2 O3 solution in cryolite is electrolyzed using carbon as the cathode and anode. Reaction: Anode: carbon rod 3 O2–(l) O2 (g) + 6 e– Cathode: iron vessel coated with carbon 2 Al3+(l) + 6 e– 2 Al(l) The resulting Al2 O3 can be used as follows.   To demolish buildings made of iron or steel. This is due to the formation of Al2 O3 which is very exothermic (resulting in a temperature of 3,000 °C), so it is able to bind oxygen from other metal oxides. b. If Al2 O3 is mixed with transition metals, gems will formcolorful, such as: · Rubies, red gems formed from Al2 O3 and Cr3+. · Sapphire, a blue gem formed from Al2 O3 , Fe2+, and Ti4+. · Topaz, a yellow gem formed from Al2 O3 and Fe2+. · Amethyst, a purplish-brown gem formed from Al2 O3 and Mn3+. Uses of aluminum include:         Aluminum is a metal that is light, strong and corrosion resistant, so it is widely used for household equipment, window frames, and even building frames. Biscuit, chocolate and cigarette packaging coating. The metal mixture of 90% Al and 10% Mg (magnalium) is strong and light, only used in making airplanes. A mixture of 20% Al, 50% Fe, 20% Ni, and 10% Co can be used asvery strong magnet. Alum (KAl(SO4 )), is used as a water purifier and anti-sweat agent. Al(OH)3 is used to neutralize excessive stomach acid. Thermite (a mixture of Al and Fe2 O3 ) is used to weld metal. Aluminum sulfate is used in textile dyeing.