C4 - Extracting metals and equilibria

• Dynamic equilibrium


  Forward and backwards reactions happen at the same rate

  Concentration of all reacting substances do not change
• Increase in temperature in a reversible reaction


  The position of equilibrium moves in the endothermic reaction.

  Reaction takes in the energy provided from the heat.
• Increase in pressure in a reversible reaction


  The position of equilibrium moves to the side with fewer moles.

  Reduces the pressure back down.
• The use of a catalyst in a reversible reaction 


  
  

  Reduces the amount of activation energy required for the reaction to start
• Closed system


  No substances can enter or leave
• Exothermic reaction


  Reaction that gives out energy
• Endothermic reaction


  Reaction that takes in energy
• (+ energy) Endothermic = backwards reaction
• (+ energy) Exothermic = forward reaction
• Shells ' shield ' the electrostatic forces between the positive metal ions and delocalised electrons.
• Le chatelier's principle

  Changing the conditions in a reversible reaction means the position of equilibrium will shift to counteract the change 
• Decrease in temperature in a reversible reaction


  The position of equilibrium moves in the exothermic reaction.

  Reaction releases heat energy to counteract change
• Decrease in pressurein a reversible reaction


  The position of equilibrium moves in the to the side with more moles to increase the pressure again
• Increase in concentration in a reversible reaction


  The position of equilibrium moves to the side of less concentration.

  Increases the yield of the other side
• Metal reacts with cold water

  Metal hydroxide and hydrogen gas
• 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
• Metal reacts with dilute acid


  Salt and hydrogen
• Metal reacts with cold water


  Suggests the metal is very reactive as only the most reactive metals can react with cold water
• 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 using displacement to compare reactivity of two metals


  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
• 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
• Displacement reaction


  Reduction and oxidation are taking place in the same reaction

  • more reactive metal atoms lose electrons to form ions (oxidation)
  • less reactive metal ions gain electrons to form the element (reduction)
• Reactivity of a metal


  Tendency to form cations (positive ions)
• Metals highest in the reactivity series are most easily oxidised
• Most metals are extracted from ores found in the Earth's crust
• Ore


  A rock which contains metals often chemically combined with other substances
• Unreactive metals are found in the earth's crust as uncombined elements
• Oxidation (in terms of oxygen)


  Gain of oxygen
• Reduction (in terms of oxygen)


  Loss of oxygen
• Most ores contain metals chemically combined with oxygen

  • Process to extract the metal is reduction
• 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
• 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

  • plants take up metals through their roots
  • 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

  • bacteria produce solutions called leachates containing the metals
  • Scrap iron can be used to remove the metal from the leachate