Electrolysis Revision mat

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  • C3 - Electrolysis
    • Electrolytes
      • It is the thing being sperated
      • They are ionic substances in the molten state or dissolved in water
    • Ions
      • Positively charged cations migrate to the negatively charged cathode
      • Negatively charged anions go to the positively charged anode
    • OILRIG
      • Oxidation Is Loss of electrons
        • Occurs at the anode
      • Reduction Is Gain of electrons
        • Occurs at the cathode
    • Sodium manufacture
      • Created by the electrolysis of molten sodium chloride
      • Sodium is produced at the negative cathode
        • Sodium can be used in street lamps and as a coolant in some nuclear reactors
      • Chlorine is produced at the positive anode
      • Half Equations:
        • Cathode: Na+ + e-   --> Na
          • The ions are reduced to become sodium atoms
        • Anode: 2Cl-   --> Cl2  + 2e-
          • The ions are oxidised and pair up to form chlorine molecules
      • Molten lead bromide is electrolysed in the same way - except molten lead bromide is the electrolyte
        • Cathode = lead (liquid)
        • Anode = bromine (gas)
    • Electrolysis of aqueas solutions
      • Molten ionic salts only contain the ions of the salt
        • But dissolve the salt in water and there are H+ and OH- ions from the water aswell. This can make things more interesting.....
      • At the anode the simplest ion is discharged... e.g. Cl- is discharged not OH-
      • At the cathode a metal will be discharged if it's less reactive than hydrogen.
        • If it is more reactive hydrogen is discharged... e.g. Copper is less reactive than hydrogen so it will be discharged at the cathode during electrolysis of aqueous copper salts
    • Formation of products in electrolysis using inert electrodes
      • Inert electrodes are made of unreactive material so they don't take part in the reaction
      • Copper chloride solution , CuCl2
        • Cathode = Copper (s)
        • Anode = Chlorine (g)
      • Copper sulfate solution, CuSO4
        • Cathode = copper (s)
        • Anode = Oxygen (g)
      • Sodium sulfate solution, Na2SO4
        • Cathode = Hydrogen
        • Anode = Oxygen
      • Sodium chloride solution, NaCl
        • Cathode = Hydrogen (g)
        • Anode = chlorine  (g)
    • Making pure copper
      • The mass of the anode decreases during the electrolysis
      • The mass of the cathode increases as the pure copper is attracted to it
      • The anode is made of impure copper and the pure copper is attracted to the cathode where pure copper is then created
      • Any impurities form as sludge under the anode
    • Electroplating
      • This can be used for 2 reasons
        • It can Improve the appearance of something
        • It can protect a metal object and make it more resistant to corrosion


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