electrolysis

• during electrolysis an electric current is passed through an electrolyte, the ions move towards the electrodes, where they react and the compound decomposes
• what is an electrolyte?


  a molten r dissolved ionic compound
• the positive ions in the elctrolyte will move towards the cathode (-ve electrode) and gain electrons (are reduced)
• the negative ions in the electrolyte will move towards the anode (+ve electrode) and gain electrons (they are reduced)
• an ionic solid cannot be electrolysed as the ions are in fixed positions and cannot move
• molten ionic liquids are always broken up into their elements:


  positive metal ions are reduced at the cathode

  negative nonmetal ions are oxidised to the element at the anode
• molten ionic compunds can be electrolysed as the ions can move freely and conduct electricity
• metal extraction via elctrolysis: aluminium is extracted from the ore bauxite by electrolysis


  • aluminium oxide has a very high melting point so it is mixed with cryolite to lower its melting point
  • the molten mixture contains free ions so itll conduct electricity
  • the positive Al3+ ions are atrracted to the cathode where they will pick up three electrons and turn into neutral aluminium atoms, they then sink to the bottom of the tank
  • the negative O2- ions are attracted to the anode where they then lose 2 electrons, they netrual O atoms will then combine to form positive O2 molecules
• in aqueous solutions as well as the ions from the ionic compound there will be hydrogen ions (H+) and hydroxide ions (OH-) from the water
• (in aqueous solutions)

  at the cathode if H+ ions and metal ions are present, hydrogen gas will be produced if the metal ions form an elemental metal that is less reactive than hydrogen, if the metal ions form an elemental metal that is less reactive than hydrogen a solid layer of the pure metal will be produced instead
• (in aqueous solutions )

  at the anode if OH- and hallide ions are present molecules of chlorine, bromine or iodine will be formed. if no halide ions are present then the OH- ions are discharged and oxygen will be formed