Equilibria + Metal Extraction

Metal Extraction
1. Metals are found in their ores, and in order to get the pure metal from the ore, you need to find a way to get rid of the impurities
  1. Roasting is a technique used to convert sulphide ores to the metal oxides
    1. e.g. 2ZnS + 3O2------> 2ZnO + 2SO2
      1. The only problem is that it creates SO2 which is a pollutant, however, this can then be converted to H2SO4 and sold off as a means of higher profits
2. Extraction of Iron
  1. The iron ore is known as Haematite Fe2O3
  2. The method of extraction is reduction with carbon
    1. The process occurs in a blast furnace
    2. 1. Coke (impure carbon) reacts with oxygen to produce CO2
      1. An exothermic reaction so maintains heat in the furnace
      2. 2. CO2 produced reacts with more coke to produce carbon monoxide
        This is the reducing agent
        C + CO2 ----> 2CO
        An endothermic reaction
        The CO reduces the haematite to iron
        (Fe2 (+3) + 3e- ----> 2Fe (0)) x2
        (CO ------> CO2 + 2e-) x3
        Overall: 2FeO3 + 3CO -------> 2Fe + 3CO2
        The carbon dioxide could be used to make more reducing agent
        By reacting with more coke
        The iron will sink to the botton of the furnace to be tapped off
        Removing Impurities
        The main impurity in this is silicon dioxide
        This can be removed by adding calcium carbonate
        The calcium carbonate will decompose into calcium oxide
        The calcium oxide will react with the silicon dioxide to form calcium silicate
        This can be used for breeze blocks, tar
        CaO + SiO2 -------> CaSiO3
        CaCO3-----> CaO + CO2
        Haematite could even react with the carbon: Fe2O3 + 3CO ------> 2Fe + 3CO
        More reducing agent also produced
  3. Advantages:
    1. Heat is mainatined by the exothermic reaction
    2. Raw materials are fairly cheap
    3. A continous process
  4. Disadvantages:
    1. Releases CO2- contributes to GW
    2. Doesn't produce pure iron
      1. Not really a bad thing because pure iron is brittle
3. Extraction of aluminium
  1. This is done by electrolysis
    1. It is too reactive to be reduced by chemical means
  2. The aluminium ore is called bauxite and is very common (Al2O3)
  3. Purification
    1. The ore is dissolved in NaOH
      1. Silicon dioxide found as an impurity in the ore will not dissolve
        It is filtered off to remove the SiO2
  4. Electrolysis
    1. Both the anode (positively charged) and cathode (negatively charged) are made of carbon graphite
    2. Cryolite (Na2AlF6) is added to lower the melting point of the ore from around 2000 to 700 degrees celcius
    3. At the anode
      1. 2O (2-) ------> O2 + 4e-
        Oxidation
    4. At the cathode
      1. Al (+3) + 3e- -------> Al
        Reduction
    5. Overall: 2Al2O3-----> 4Al + 3O2
    6. Aluminium formed at the cathode will sink to the bottom and be tapped off
    7. The O2 formed at the anode may react with the carbon to produce CO2
  5. Advantages:
    1. A continuous process
    2. Pure aluminium formed
  6. Disadvantages:
    1. Expensive because it's energy intensive
    2. Only works for ionic oxides
4. Extraction of Titanium
  1. Titanium ore: Rutile, TiO2
    1. The ore has many uses on its own
      1. Paints, paper, milk, polymers, sunscreens etc
  2. Titanium uses:
    1. Hip replacements
  3. Properties
    1. Low density
      1. High strength
        resistant to corrosion
  4. We can't use carbon as a reducing agent because it will form titanium carbide which is very brittle
    1. To avoid this, we need to chlorinate the TiO2 to form TiCl4. This is done by heating the ore and chlorine in the presence of coke
      1. TiO2+ 2Cl2 + C------> TiCl4 + 2CO
        The Cl2 is reuced and the C is oxidised. However, the Ti has not been changed
        We now have TiCl4 which needs to be reduced. I.e.the chloride ion needs to be reduced
        Conditions:
        550 degrees c
        Exothermic reaction so not much heat is needed
        An inert atmosphere of argon so the TiCl4 doesnt react with oxygen to form the ore again
        TiCl4 is to be vapourised
        Reducing agent: Mg or Na
        Overall equation:
        TiCl4 + 2Mg ------> MgCl2 + Ti
        Half eq
        Ti (4+) + 4e- ------> Ti (0)
        Mg------ Mg (2+) + 2e-
        TiCl4 + 4Na -------> Ti + NaCl
        Half eq
        Ti (4+) + 4e- ------> Ti
        Na ------> Na + e-
        Sealed container
  5. Advantages: Pure titanium
    1. Exothermic
  6. Disadvantages: Batch Process
5. Extraction of tungsten
  1. Use: Light bulb filaments
  2. Properties: High density, high temp resistant
  3. Ore: WO3
    1. Reducing agent: H2 gas
      1. Overall Eq:
        WO3 + 3H2 ------> W + 3H2O
      2. High temp required
  4. Advantages: Pure tungsten produced
    1. Reducing agent is cheap
  5. Disadvantages: H2 is flammable
    1. Expensive: Energy intensive
Dynamic Equilibria
1. Dynamic: A reaction that goes forward and backwards
2. Equilibria: Where the forward and backwards reaction takes place at the same speed
  1. A closed system
    1. The conc of the reactants and products are constant
3. Where both the forward and backward reactions are taking place at the same rate
4. The position of equilibria can be shown on a diagram
5. A catalyst will not affect the position of the equilibria, all it does is it reduces the time it takes to get to the equilibrium
  1. This is because it speeds up both the forward and backward reaction
6. LeChatiliers principle: This is the idea that if change the conditions of an equilibrium, then the equilirbium system will move to oppose that change.
  1. E.g. if you make it warmer, the equilibrium will move to make it cooler
7. Examples:
  1. The haber process:
    1. N2 + 3H2--------> 2NH3 (-92 kJmol-1)
      1. Conditions:
        High pressure: You get more yield as the equilibrium system will try and oppose the change and produce more of the side with fewer partices i.e. more product
        Around 20000kPa
        Dangerous
        Expensive
        Ideally, Lower: Decreasing temp mean system will try and oppose it and increase the temp by forcing reaction in the exo direction which id the forward direction
        But then that means a lower rate of reaction so a compromise of around 380-450 is used
        Products tapped off and reactants continuously fed in, favour forward reaction due to lechatiliers principle
  2. Hydration of Ethene
    1. C2H4 + H2O -------> C2H5OH (-461kJmol-1)
      1. High pressure (6500kPa)
        Ideally low temp but a compromise is used for a high rate of reaction (570 k)
        Conc: Compromised: You dont want too much in there because addition polymerisation takes place and thos blocks the active site of the catalyst
        Also, too much water will dilute the catalyst
        However, a lower conc means a lower rate of reaction
  3. Production of methanol
    1. CO + 2H2 ------> CH3OH (-91kJmol-1)
      1. High pressure (10000 kPa)
        Compromised temp of 500k
        Uses: Perspex glasses, bus windows, chemical feedstock

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Equilibria + Metal Extraction

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	Created by bilkis-21 almost 11 years ago