Mercury and copper, which belong to the least reactivity series, are often found in the form of their sulphide ores. Cinnabar (HgS) is the ore of mercury. Copper glance (Cu2S) is the ore of copper.
Extraction of mercury metal: Cinnabar (HgS) is first heated in air. This turns HgS [mercury sulphide or cinnabar] into HgO (mercury oxide); by liberation of sulphur dioxide.
Mercury oxide so obtained is again heated strongly. This reduces mercury oxide to mercury metal.
2HgS + 3O2 ⇨ 2HgO + 2SO2
2HgO ⇨ 2Hg + O2
Extraction of copper metal: Copper glance (Cu2S) is roasted in the presence of air. Roasting turns copper glance (ore of copper) into copper (I) oxide. Copper oxide is then heated in the absence of air. This reduces copper (I) oxide into copper metal.
2Cu2S + 3O2 ⇨ 2Cu2O + 2SO2
2Cu2O + Cu2S ⇨ 6Cu + SO2
Iron, zinc, lead, etc. are found in the form of carbonate or sulphide ores. Carbonate or sulphide ores of metals are first converted into respective oxides and then oxides are reduced to respective metals.
Extraction of zinc: Zinc blende (ZnS: zinc sulphide) and smithsonite or zinc spar or calamine (ZnCO3: zinc carbonate) are ores of zinc. Zinc blende is roasted to be converted into zinc oxide. Zinc spar is put under calcination to be converted into zinc oxide.
2ZnS + 3O2 ⇨ 2ZnO + 2SO2
ZnCO3 ⇨ ZnO + CO2
Zinc oxide so obtained is reduced to zinc metal by heating with carbon (a reducing agent).
ZnO + C ⇨ Zn + CO
Extraction of iron from Hematite (Fe2O3): Hematite ore is heated with carbon to be reduced to iron metal.
Fe2O3 + 3C ⇨ 4Fe + 3CO2
Extraction of lead from lead oxide: Lead oxide is heated with carbon to be reduced to lead metal.
2PbO + C ⇨ 2Pb + CO2
Reduction of metal oxide by heating with aluminium: Metal oxides are heated with aluminium (a reducing agent) to be reduced to metal. Following is an example:
Manganese dioxide and copper oxide are reduced to respective metals when heated with aluminium.
3MnO2 + 4Al ⇨ 3Mn + 2Al2O3
3CuO + 2Al ⇨ 3Cu + Al2O3 + heat
Thermite Reaction: Ferric oxide; when heated with aluminium; is reduced to iron metal. In this reaction, lot of heat is produced. This reaction is also known as Thermite Reaction. Thermite reaction is used in welding of electric conductors, iron joints, etc. such as joints in railway tracks. This is also known as Thermite Welding (TW).
Fe2O3 + 2Al ⇨ 2Fe + Al2O3 + heat
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