Extracting metals and Equilibria

• Products when a metal reacts with cold water

  Metal hydroxide and hydrogen gas
• Products when a metal reacts with steam

  Metal oxide and hydrogen gas
• Reaction when calcium reacts with cold water

  Ca + 2H2O → Ca(OH)2 + H2
• Reaction when zinc reacts with steam


  Zn + H2O → ZnO +H2
• Products when a metal reacts with dilute acids

  Salt and hydrogen
• If a metal reacts with cold water

  It suggests the metal is very reactive as only the most reactive metals can react with cold water
• A metal reacts with oxygen but not acid or cold water


  Not very reactive, most metals react with oxygen
• Metal which will not react with water, acid or oxygen

  • Gold
• Experiment to compare reactivity of two metals using displacement


  1. Add a solid metal to a salt solution (the salt must contain a different metal)

  2. If the solid metal is more reactive, it will gradually disappear, displacing the metal that was in the salt solution

  3. If nothing happens, the metal in the salt is more reactive and can't be displaced
• When magnesium is added to copper sulfate solution

  The copper sulfate solution is blue. Magnesium is more reactive than copper so when magnesium is added the blue solution decolourises and copper coats the surface of the magnesium
• Why a displacement reaction can be called a redox reaction

  A redox reaction occurs when reduction and oxidation are taking place in the same reaction. In a displacement reaction, the more reactive metal atoms lose electrons to form ions (oxidation) and the less reactive metal ions gain electrons to form the element (reduction)
• Reactivity of a metal is related to its tendency to form


  Cations (positive ions)
• Metals most easily oxidised


  The metals highest in the reactivity series. More reactive metals are more likely to react with water and dilute acids to form cations
• Where most metals are extracted from

  From ores found in the Earth's crust
• Ore


  A rock which contains metals often chemically combined with other substances
• Metals found in the earth's crust as uncombined elements

  Unreactive metals
• Oxidation in terms of oxygen

  Gain of oxygen
• Reduction in terms of oxygen

  Loss of oxygen
• Methods to extract metals from their ores

  • Reduction with carbon
  • Electrolysis
• Extracting iron from its ore

  1. Iron is less reactive than carbon so can be extracted by reduction with carbon

  2. Electrolysis could also be used, but this would use a lot of unnecessary energy (high cost)
• Chemical equation for reduction of iron with carbon


  2Fe2O3 + 3C → 4Fe + 3CO2
• Extracting aluminium from its ore

  1. Aluminium is more reactive than carbon so electrolysis must be used

  2. When the molten ore undergoes electrolysis, the metal forms at the cathode
• Why aluminium oxide is dissolved in molten cryolite when extracting aluminium

  Aluminium oxide has a very high melting point. It is dissolved in molten cryolite to produce an electrolyte with a lower melting point, reducing energy usage and cost
• Phytoextraction - using plants to extract metals


  Plants are grown in areas with metals in the soil. The plants take up metals through their roots and concentrate them in their shoots and leaves. These plants are burned and the metals are removed from the ash
• Bacterial extraction of metals

  Some bacteria absorb metal compounds. These bacteria produce solutions called leachates containing the metals. Scrap iron can be used to remove the metal from the leachate
• Limitations of biological methods of extraction
• Phytoextraction


  1. Plants are grown in areas with metals in the soil

  2. The plants take up metals through their roots and concentrate them in their shoots and leaves

  3. These plants are burned and the metals are removed from the ash
• Bacterial extraction


  1. Some bacteria absorb metal compounds

  2. These bacteria produce solutions called leachates containing the metals

  3. Scrap iron can be used to remove the metal from the leachate
• Limitations of biological methods of extraction

  • Only suitable for low grade ores with smaller quantities of metals
  • Slow processes
  • Require displacement or electrolysis for the final step
• Oxidation


  The loss of electrons
• A metal's position in the reactivity series


  Its relative resistance to oxidation
• Metals lower in the reactivity series are less reactive, so they are less likely to form their cations and are more resistant to oxidation
• Advantages of recycling metals

  • Economically beneficial because electrolysis is expensive
  • Prevents the detrimental environmental impact of mining and extraction of new metals
  • Less waste produced so less landfill
  • Less energy required compared to electrolysis
  • More sustainable - not using up the finite resources
  • Recycling process provides employment
• Life cycle assessment


  Analysis of the overall environmental impact that a product may have throughout its lifetime
• Factors considered in a life cycle assessment

  • Extraction and processing of raw materials
  • Manufacturing
  • Packaging and transportation
  • Use of the product
  • Disposal
• Reversible reaction


  A reaction in which the products can react to form the original reactants
• Reversible reactions are denoted by the symbol: ⇌
• Changing the direction of a reversible reaction


  Changing the reaction conditions (e.g. temperature, pressure, concentration)
• Dynamic equilibrium


  When the rate of the forward reaction equals the rate of the backwards reaction, so the concentration of reactants and products are constant even though compounds are continually reacting
• Closed system


  A system where nothing is added or removed, so all reactants and products remain in the reaction vessel