Unit 14: Metal extraction

Unit 14: Metal extraction

1. Use the reactivity series to explain why some metals are extracted using carbon

   • The way we extract a metal from its ore depends on the position of the metal in the reactivity series. Carbon is used to reduce oxides of metals below it in the reactivity series.

2. Use the reactivity series to explain why some metals are extracted by electrolysis

   • Metals above carbon in the reactivity series cannot be extracted from their oxides by heating with carbon. This is because the metal bonds to oxygen too strongly and the carbon is not reactive enough to remove it. So we have to use electrolysis.

3. Describe the extraction of zinc from zinc blende

   • Raw materials: zinc blende, coke (carbon) and air. Ore is first crushed and treated to remove impurities. Ore is then strongly heated in air to form zinc oxide. Zinc oxide is heated with coke in a blast furnace. Blast of air is blown into bottom of furnace. Excess carbon reacts with oxygen in air to form carbon monoxide. Higher up in the furnace, carbon monoxide reduces zinc oxide to zinc.

4. Name an ore of aluminium and an ore of iron

   • Bauxite is the ore of aluminium
   • Haematite is the ore of iron

5. Name the raw materials required for extracting iron in a blast furnace

   • iron ore (haematite), coke (carbon), limestone and air

6. Describe the reactions occuring in the blast furnace, including formation of slag

   • 1. At the bottom of the furnace the coke burns in the hot air blast to form carbon dioxide. This exothermic reaction releases heat which helps heat the furnace: C(s) + O2(g) -----> CO2(g)
   • 2. The carbon dioxide reacts with the coke to form carbon dioxide: CO2(g) + C(s) -----> 2CO(g)
   • 3. The carbon monoxide reduces the iron(III) oxide to iron: Fe2O3(s) + 3CO(g) -----> 2Fe(l) + 3CO2(g)
   • 4. The iron flows to the bottom of the furnace and is removed as a liquid. It flows into moulds and is left to solidify. The hot waste gases exiting from the top of the furnace are used to heat the air going into the furnace, thus reducing energy costs.
   • 5. The heat from the furnace decomposes the limestone: CaCO3(s0) -----> CaO(s) + CO2(g). The calcium oxide reacts with the silicon(IV) oxide from haematite to form a 'slag' of calcium silicate: CaO(s) + SiO2(l) -----> CaSiO3(l). The liquid slag runs down and forms a layer on top of the iron because it has a lower density than iron. The slag is run off and the solid is used as building material.

7. Describe the conversion of iron into steel

   • 1. Molten iron and scrap iron are poured into the converter. A water-cooled tube called an oxygen lance is lowered into the converter. Oxygen and powdered calcium oxide are blown onto the surface of the molten iron through the lance.
   • 2. The oxygen oxidises carbon, sulfur, silicon and phosphorus to their oxides. The carbon dioxide and sulfur dioxide escape from the converter because they are gases. These exothermic reactions release heat which keeps the iron molten. Silicon and phosphorus oxides are solids and acidic oxides. So these react with the powdered calcium oxide which is basic. A slag is formed. The slag floats on the surface of the molten iron and is removed.
   • 3. The amount of carbon in the steel is controlled by the amount of oxygen blown into the impure iron. The longer the oxygen blast, the more carbon is removed. After the required amount of carbon has been removed, other elements such as chromium and nickel are added to make particular types of steel.

8. Explain why basic oxides and oxygen are needed to convert iron into steel

   • To get rid of the impurities

9. Describe why the steel alloys are used for particular jobs rather than pure iron

   • Pure iron is too soft and weak to be very useful. Steel is an alloy of iron with carbon or carbon and other metals. This makes it stronger and harder because the atoms from carbon and other metals stop the layers from sliding over each other.

10. Explain why alloys have particular properties by reference to their structure

    • Mild steel is low carbon steel. It is soft, malleable and ductile. It is harder than pure iron because the carbon atoms alter the structure so that the layers do not slide as easily.
    • Stainless steels are high alloy steels. They are very strong and resist corrosion. This is because the chromium atoms stop the layers from sliding over each other.

11. Name some uses of aluminium, mild steel and stainless steel

    • Aluminium
      • used for making aircraft bodies, some food containers, cooking foil
    • Mild steel
      • to make car bodies, parts of machinery, buildings, general engineering purposes
    • Stainless steel
      • used in the construction of pipes and towers in chemical factories, cutlery, surgical instruments

12. Name some uses of zinc and copper

    • Zinc
      • used to galvanise iron or mild steel to prevent rusting
    • Copper
      • electrical wiring, bases of cooking pans

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