Electrolysis

A mindmap for unit 6 of the CIE IGCSE Chemistry specification, 'Electricity and Chemistry'. 

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  • Created by: steph
  • Created on: 19-03-13 18:50
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  • Electrolysis
    • What is it?
      • Breaking down of a compound using electricity
        • Decomposing
      • Ionic compounds
        • Molten or dissolved in water
    • Electrolysis cell
      • Electrolyte
        • The compound that conducts electricity and breaks down
      • Electrodes
        • Carry electric current to and from electrolyte
        • Inert
          • Graphite  or platinum
          • Do not react with electrolyte or electrolysis products
        • Anode
          • Positive electrode
          • Halogens or oxygen forms
          • Oxidation
            • Loss of electrons
          • Anions: negative
    • Anode
      • Positive electrode
      • Halogens or oxygen forms
      • Oxidation
        • Loss of electrons
      • Anions: negative
    • Cathode
      • Electrodes
        • Carry electric current to and from electrolyte
        • Inert
          • Graphite  or platinum
          • Do not react with electrolyte or electrolysis products
      • Negative electrode
      • Metal or hydrogen  forms
      • Reduction
        • Gain of electrons
      • Cations: positive
    • Aqueous sodium chloride
      • Ionic compounds in water have more ions
      • H+, OH-, Na+, Cl-
      • Ion dischange series
        • Lower down series = more likely it will be discharged
        • Positive ions
          • Na +, Mg 2+, Al 3+, H +, Cu 2+
        • Negative ions
          • SO4 2-, NO3 -,  OH -, Cl -, Br -, I -
      • Anode
        • Chloride ions lose electrons
        • 2Cl -(aq) -> Cl2 (g) + 2e -
      • Cathode
        • Hydrogen ions accept electrons
        • 2H +(aq) + 2e - -> H2 (g)
      • Na + and OH - remain in solution
        • Aqueous sodium hydroxide formed
    • Dilute aqueous solutions
      • OH - is lower in series than sulfate
        • Oxygen discharged
    • Refining copper
      • Impure copper = anode
        • Copper atoms lose valency, form copper ions
      • Pure copper = cathode
        • Copper ions in electrolyte gain electrons, forms copper
      • Copper sulfate (II) solution = electrolyte
        • Remains the same colour due to the ions in solution being replaced
      • Inert electrodes
        • Anode can't lose electrons
          • Hydroxide ions discharged, oxygen forms
        • Copper deposited at cathode
        • Electrolyte loses its colour
    • Electroplating
      • Object to be electroplated at cathode
      • Plating metal as the anode
      • Electrolyte is a solution of ionic compound of the plating metal
      • Uses
        • Protection from corrosion
        • Improving appearance
    • Aluminium extraction
      • Bauxite = ore
      • Dissolved in molten cryolite
      • Cathode:  aluminium ions gain electrons, reduced to aluminium
      • Anode: oxide ions lose electrons, oxidised to oxygen

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