C6

• electrolysis is splitting ionic substances into their elements using electricity

  electron from the metal (usually) transferred to anode, then transported along the wire to cathode through the power of the battery
• Electrolytes:

  • when ionic compounds are melted/dissolved in water, ions are free to move and carry charge so the solution conducts electricity
  • these are called electrolytes
• Electrodes:

  • when voltage (direct current/dc) is applied to an electrolyte, the charged ions are attracted to the oppositely charged electrode
  • positively charged ions are attracted to negative electrode (cathode)
  • negatively charged ions are attracted to positive electrode (anode)
  • when an ion touches an electrode, electrons can be transferred, creating an element
• Anode:

  • = oxidised
  • oxygen/halogen forms at carbon anode, C and O react to form CO2
  • usually made of carbon as good conductor and cheap
  • if halide is present, halogen will form - if not, oxygen will form
• Cathode:

  • = reduced
  • metal forms at cathode
  • if hydrogen is less reactive than the metal, then hydrogen forms at the cathode

  Disadvantages of electrolysis - high energy costs, electrodes need replacing, must keep solution molten, energy needed to produce electrical current
• Electrolysis of Aluminium Oxide:

  • splits metal oxide into pure metal and oxygen
  • Al2O3 is a solid found in the ore bauxite, so hard to extract and ions aren’t free to move and carry charge
  • must be purified from bauxite to produce Al2O3, then mixed with cryolite to reduce MP but still v. high MP so lots of energy needed
  • for this specific one, electrodes made of carbon
  • Al3+ and O2- in electrolyte
  • after Al3+ + 3e- → Al, it drops to the bottom of beaker as molten aluminium metal
  • overall equation = 2Al2O3 (l) → 4Al (l) + 3O2 (g)
• Of aqueous solutions:

  • apart from metal and non-metal in electrolyte, there will be H+ ions and OH- ions from the water bc. H2O (l) → H+ (aq) + OH- (aq)
  • cathode will attract metal and H+ ions, but only discharge the least reactive one (if the metal is less reactive than hydrogen, it won’t be discharged and instead accumulate around the cathode)
  • anode will attract non-metal and OH- ions, but will only discharge one (if a halide[halogen] is present, it’ll be discharged, but if not then OH- will) → but OH- will be discharged as oxygen bc. the hydrogen will mix in/become H2O