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  2. METAL CHEMISTRY N4 N5 CHEMISTRY CHEMISTRY OBTAINING METALS After completing this topic you should be able to : • State ores are naturally occurring compounds of metals. • State the less reactive metals, including gold, silver and copper, are found uncombined in the Earth’s crust and the more reactive metals have to be extracted from their ores. • Explain why some metals can be obtained from metal oxides by heat alone; some metal oxides need to be heated with other substances, e.g. carbon or carbon monoxide; other metals cannot be obtained by these methods. • Describe how iron is produced from iron ore in the Blast Furnace. • Give examples of the important uses of alloys, e.g. brass, solder, “stainless” steel. • Describe the extraction of metals from compounds as a reduction reaction.N5 • Describe the reaction taking place at the negative electrode during electrolysis for the extraction of metal as a reduction reaction. N5

  3. OBTAINING METALS The metals we use are obtained from rocks in the Earth’s crust. Most metals are too reactive to exist in a pure uncombined form in the Earth’s crust. Metals are found as in rocks metal compounds. The usual metal compounds found in rocks are OXIDES, SULPHIDESandCARBONATES. NATIVE METALS A few metals are found uncombined, as they are very unreactive. Metals, which are found uncombined are called NATIVE METALS. The native metals are: Platinum(Pt) Copper(Cu) Silver(Ag) Gold(Au)

  4. METAL ORES Rocks, which contain metals or compounds of metals are called ORES. As man’s knowledge of chemistry increased more metals were discovered, as ways of extracting metals were found. Using the N5 Chemistry Data Booklet; complete the REACTIVITY SERIES OF METALSwith the Date of Discovery in your notes. REACTIVITY SERIES OF METALS METAL DATE OF DISCOVERY potassium sodium lithium calcium magnesium aluminium zinc iron tin lead copper mercury silver gold 1807 1807 1817 1808 1808 1825 Ancient Ancient Ancient Ancient Ancient Ancient Ancient Ancient CONCLUSION The least reactive metals were discovered the earliest. Using the information on metal ores in the following slides; complete the EXAMPLES OF METAL ORES table in your notes.

  5. EXAMPLES OF METAL ORES NAME OF METAL COMPOUND IN ORE NAME OF ORE METAL IN ORE iron sulphide iron Iron pyrites(Fools Gold) copper copper carbonate Malachite lead lead sulphide Galena

  6. EXAMPLES OF METAL ORES NAME OF METAL COMPOUND IN ORE NAME OF ORE METAL IN ORE aluminium oxide aluminium Bauxite iron iron(III) oxide Haematite(Blood Stone) tin tin(IV) oxide Cassiterite

  7. METALOXIDES A large number of ores contain metal oxides. To extract a metal from an ore requires heat. Some metal oxides break down by heat alone. HEATING SILVER(I) OXIDEANDCOPPER(II) OXIDE RESULTS SILVER(I) OXIDE COPPER(II) OXIDE Silver(I) oxidebreaks down on heating to form silver and oxygen. silver(I)oxide copper(II) oxide Heating has no effect oncopper(II) oxide. HEAT HEAT

  8. N5 Breaking down a compound into its elements from which it is made is called a DECOMPOSITION REACTION. CHEMISTRY Silver(I) oxidedecomposes on heating to form silver and oxygen. heat silver(I) oxide silver oxygen + heat Ag2O 2 O2 + Ag 4 Ionic equation: heat (Ag+)2O2- Ag O2 2 + 4 The silver(I) ion is changed to a silver atom. To do this each silver(I)ion has to gain 1 electron. This change is reduction. Ag e- Ag+ +

  9. METALOXIDES WITHCARBON Metals with very low reactivity can be extracted by just heatingtheir compounds. Copperis too reactive to be extracted by HEAT ALONE. Metals with low to middle reactivity can be extracted by heating their compoundswith carbon. HEATING COPPER(II) OXIDE WITHCARBON RESULTS Drop hot test tube into cold water After the reaction some orange / brown coppercan be seen in the beaker. copper(II) oxide +carbon cold water The products of the reaction are COPPER andCARBON DIOXIDE. HEAT

  10. N5 Carbon helps remove the oxygen from the copper(II) oxide. The oxygen transfers to the carbon forming carbondioxide. CHEMISTRY heat copper(II)oxide carbon copper carbondioxide + + heat + C Cu CO2 2 2 CuO + Ionic equation: heat + C Cu CO2 2 2 Cu2+O2- + The copper(II) ion is changed to a copper atom. To do this each copper(II) ion has to gain 2 electrons. This change is reduction. Cu 2 e- Cu2+ +

  11. EXTRACTING IRON – THE BLAST FURNACE Iron ore, coke (carbon) and limestone enter the furnace from the top of the furnace. Iron is extracted from its ore using carbon. The reaction requires a lot of heat. To provide the necessary heat the reaction is carried out in a BLAST FURNACE. The extraction of the iron happens in 3 stages. STAGE 1:The coke (carbon) burns to produce carbon dioxide CO2. Molten iron flows to the bottom of the furnace. C(s) + O2(g) CO2(g) STAGE 3 STAGE 2:The CO2 from stage 1 reacts with more carbon to form carbon monoxide CO. STAGE 2 CO2(g) + C(s) 2CO(g) STAGE 1 STAGE 3:The CO from stage 2 reacts with iron(III) oxide Fe2O3 in the iron ore removing the oxygen. HOT AIR BLAST HOT AIR BLAST Fe(l) Fe2O3(s) + 3CO(s) 2Fe(l) + 3CO2(g)

  12. N5 heat CHEMISTRY iron(III)oxide carbonmonoxide iron carbondioxide + + heat + 3 CO Fe CO2 2 Fe2O3 3 + Ionic equation: heat + CO Fe CO2 2 3 3 (Fe3+)2(O2-)3 + The iron(II) ion is changed to a iron atom. To do this each iron(III) ionhas to gain 3 electrons. This change is reduction. Fe 3 e- Fe3+ +

  13. N5 OXIDATIONAND REDUCTION AGAIN!! CHEMISTRY The terms OXIDATION and REDUCTION originates from the extraction of metals industry. These terms were used for centuries before atoms and electrons were discovered. An OXIDATION reaction is a reaction where a reactant GAINS OXYGENATOMS. An REDUCTION reaction is a reaction where a reactant LOSES OXYGEN ATOMS. The extraction of iron from iron(III) oxide in the BLAST FURNACE shows these original definitions of OXIDATION and REDUCTION. heat iron(III)oxide carbonmonoxide iron carbondioxide + + heat + 3 CO Fe CO2 2 Fe2O3 3 + The iron(III) oxide hasLOSTOXYGENATOMS to produce iron. It has been REDUCED. The carbonmonoxide hasGAINED anOXYGENATOM to produce carbondioxide. It has been OXIDISED.

  14. N5 EXTRACTING ALUMINIUM CHEMISTRY Aluminium is too reactive to extract by heating with carbon or carbon monoxide. All reactive metals from aluminium upwards on the reactivity series are extracted using ELECTROLYSIS. The bauxite ore is purified to produce pure aluminium oxideAl2O3. This is called ALUMINA. Bauxite Solid ionic compound do not conduct electricity as their ions are not free to move. Alumina is dissolved in molten cryolite (Na3AlF6), as it has a lower melting point than aluminium oxide, which reduces the energy needed for the extraction. This solution is electrolysed and molten aluminium metal forms at the negative electrode. Alumina

  15. N5 CHEMISTRY Carbon positive electrodes. Carbon lining as the negative electrode. Solution of aluminium oxide in molten cryolite. Molten aluminium collects at the bottom. The aluminium ion (Al3+)moves to the negative electrode where it gains3 electrons and changes to an aluminium atom (Al). This change is reduction. Al 3 e- Al3+ +

  16. ALLOYS Often the properties of a pure metal makes it unsuitable for the purposes we wish to use it. Iron, for example, rusts easily and is quite brittle. The properties of metals can be altered, by adding small quantities of other metals, or non-metals, to make a new metal called an ALLOY. An ALLOY is a metal made by mixing different metals, or metals with non-metals. ALLOY CAR WHEEL Alloys improve the properties of metals by making them harder, stronger and more resistant to corrosion. SOLDER BRONZE STAINLESS STEEL

  17. OTHER ELEMENTSPRESENT MAIN METAL USES ALLOY Girders, cars, tools carbon iron Mild steel Stainless steel 12-carat gold Duralumin Bronze Brass Cupro-nickel Sinks, taps, cutlery iron chromium, nickel silver, copper gold Jewellery aluminium Aircraft bodywork copper, magnesium Coins, knives, swords copper tin Ornaments, bells musical instruments copper zinc nickel copper “Silver” coins