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Extraction of Aluminium

Electrolysis is used to remove Aluminium from its ore

  • Aluminium's a very abundant metal, but it is alwayts found naturally in compounds.
  • Its main ore is bauxite, and after mining and purifying, a white powder is left.
  • This is pure aluminium oxide Al2O3.
  • The Aluminium has to be extracted from this using electrolysis.

Cryolite is used to lower the temperature (and costs)

  • Al2O3 has a very high melting point of over 2000oC- so melting it would be very expensive
  • So aluminium is dissolved in moltem cryolite (which is a less common ore of aluminium).
  • Brings the temperature down to about 900oC, which makes it cheaper and easier
  • Electrodes are made of graphite whichg is a good conductor of electrisity.
  • Aluminium forms at the cathode and oxygen forms at the anode
  • Cathode:Al3 +3e- -- Al  Anode: 2O2- -- O2 +4e-
  • Oxygen then reacts with the carbon in the electrode to producr CO2. Means that Anode gradually eaten away and need replace ever so often
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Electroplating Uses Electrolysis

  • Electroplting uses electrolysis to coat the surface of one metal with another metal, 
    • Using electroplate silver onto a brass cup to make it look nice
  • Negative electrodes is the metal object you want to plate and the positive electrode is the pure metal you plated it with. you also need the electrolyte to contain ions of the plating metal.
    • To electroplate silver onto a brass cup, you'd make the brass cup, the negative electrode, a lamp of pure silver the positive electrode and dip them in a solution of silver ions e.e silver nitrate.
  • There are different uses for electroplating:
    • Decoration: sliver is attractive, but very expensive. as it is cheaper to plate a brass cup than make it out of soild silver.
    • Conduction: Metals like copper conduct electricity well the are often used to plate metals for electronic circuits and computers.
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Half Equations

  • Half equtions show the reactions at the electrodes. The main thing is to make sure the number of electrons is equal on both half- equations. 
  • For electrolysis of sodium chloride the half- equations are: 
    • Negative Electrode:
      • 2H+ + 2e- -- H2
    • Positive Electrode:
      • 2Cl- -- Cl2 - +2e-
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Useful Products from the Electrolysis of Sodium Ch

Useful Products from the Electrolysis of Sodium Chloride Solution

  • Products of the electrolysis of sodium chlorise solution are useful in industry
    • choline uses inculded:
      • production of bleach
      • plastics
    • Sodium Hydroxide is a strong alkali 
      • used widely industry in chemical industry
        • soap
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Reactivity affects the products formed by electrol

  • Somethings theres more than 2 free ions in the electrolyte.
    • if a salt is dissolved in water ther will also be some H+ and OH- Ions.
  • At the cathode if metal ions and H+ ions are present, the metal ions will stay in solution if the metal is more reactive than hydrogen. because the more reactive element the keener it is to stay as an ion so hydrogen will be produced unless the metal is less reactive than it.
  • At the postive electrode if OH- and habide ions (Cl-,Br-,I-) are present then molecules of chlorine bromine or iodine will be formed. if no halide if present oxygen will be formed.
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Electrolysis of NaCl

Common salt (NaCl) is dissolved in water aand electroylysed, it produces three useful products hydrogen,chlorine and sodium hydroxide.

  • negative electrode, two hydrogen ions accept two electrons to become one hydrogen molecule.
  • positive electrode, two chloride ions lose their electrons and become one cholrine molecule.
  • sodium ions stay in solution because more reactive than hydrogen. hydroxide ions from water are left behind. this means soium hydroxide (NaOH) is left in solution.
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  • Electrolysis is the splitting up with electricity.
  • Passing an electiric current through an ionic subtance that is ever molten or solution it will break down elements. 
  • Liquid need to coduct electricity (eletrolyte).
  • Electrolytes contain free ions (usually molten or dissolved ionic substance).
  • Free ions which conduct the electricity and allow process to work.
  • Electrial circuit to be complete needs to be a flow of electrons. electrons are taken away from ions at positive electrode and given to ions at negative electrode. ions give or lose electrons they bcome atoms or molecules and are released.
  • Reduction is a gain of electrons and oxidation is the loss of electrons.
  • Electrolysis always involves oxidation and reduction.
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Electrolysis of molten lead bromide

When salt (Lead Bromide(PbBr2)) is molten it will conduct electricity. 

At the -ve electrode one lead ion accepts two electron electrons to become one lead atom

At the +ve two bromide ions lose one electrom each and become one bromine molecule

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