Sunday, 10 January 2010

Metals

Metals The most abundant elements in the earth crust is O and Se while the most abundant metals are Al and Fe. Extraction method Exist as free element – Physical separation When the metals are extremely unreactive, it exists as free element. A mechanical separation is processed to separate metals (as free element) from rocks and sands. Water flows through the mixture, while the heavier metals sinks, lighter rocks and sands are washed away. 1) Gold Characteristic: Attractive colour resists corrosion, extremely malleable and ductile Use: Jewellery and coins 2) Silver It can exist in oxide form (Argentite) or free element. 2Ag2O→4Ag+O2 under heating. Characteristic: Attractive colour, resists corrosion, malleable, ductile and best conductor of electricity. Use: Jewellery and coins Heating alone 3) Mercury – (Cinnabar) 2HgO→2Hg+O2 by heating alone. (HgS+O2→Mg+SO2) It’s toxic, and used to make thermometer. Carbon reduction 4) Copper – (Copper pyrite CuFeS2) It becomes different oxides and sulphide when it’s exposed in air. CuS+O2→Cu+SO2 Characteristic: very good conductor of heat and electricity, very malleable and ductile, strong, non-poisonous and resists corrosion. Use: Electric wires and cooking utensils. 5) Lead – (Galena PbS) (toxic) (Roasting in air) 2PbS+3O2→2PbO+2SO2, 2PbO+C→2Pb+CO2 6) Iron – (Haematite Fe2O3 Iron(III) oxide) It’s extracted in a blast furnace. Limestone, coke, limestone are used. Chain of reaction: (1) C+O2→CO2 (2)CaCO3→CaO+CO2 (3)C+CO2→2CO (4)3CO+Fe2O3→2Fe+3CO2 Carbon monoxide is very reactive such that it have to be produced inside the blast furnace. It’s used to take away the oxygen in the iron ore quickly. Iron(II) sulphide: 4FeS+7O2→2Fe2O3+4O2, 2Fe2O3+3C→4Fe+3CO2 Characteristic: Strong, malleable, ductile and cheap (abundant) Use: Bridges, ships and gratings. 7) Zinc – (Zinc blende ZnS) Roast in air: 2ZnS+3O2→2ZnO+2SO2, 2ZnO+C→2Zn+CO2 Electrolysis of molten ore The ore is molten and put in a machine which positive graphite electrodes is placed up to attract the oxygen. The negative graphite electrode is placed down to attract the molten ore. 8) Aluminium – Bauxite Characteristic: light but strong, resists corrosion (oxide protection) Use: aeroplanes and window frames 9) Magnesium – Magnesite 10) Sodium is from rock salt (NaCl) 11) Potassium – Carnallite Other important metals and their uses 12) Tin as coatings of other metals since it’s malleable, non-poisonous, resists corrosion and offers a clean adhesive surface for paints. 13) Titanium is used to make supersonic aircraft and space vehicles; it’s also used for too implants and replacement hip joints since it’s very light and strong, having a high M.P., resist corrosion, can be easily shaped and biocompatible (non-poisonous and not rejected by the body) 14) Tungsten is used to make light bulb filaments for the high M.P. which emits white light when it’s still at solid state. The ease of extraction (reactivity) affects the year of discovery. Currently the resource of iron is the most abundant and lasting among metals. But since metals are non-renewable, limited with increasing demand, we should conserve them. -Extraction of ores, uses lots of water, with emitting lots of SO2 and CO2 -The 4Rs: reduce, reuse, recycle and replace. -Recycling of metals refers to melting down used and scrap metals, and use them again. Recycling metals saves more than a half of energy (Al 95%) while comparing to extracting them. The benefits include less metal resources and fuel can be reduced. Also less air pollutants are emitted. The public awareness of conservation can be raised. However, there’re some problems in recycling, including the difficulties to collect the waste metal, cost of transporting, cost of melting and purifying, as well as disposing waste in the process. They’re not cheap. Recycling industry is still seeking improvements. Reactivity of metals refers to the note. It's ready for now)

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