electrolysis

• Electrolysis


  The process of using electricity to break down ionic compounds into their elements or simpler compounds
• Electrolysis


  1. Ions move to the electrodes

  2. Positive ions gain electrons at the cathode

  3. Negative ions lose electrons at the anode
• Electrolysis of molten ionic compounds

  • Positive metal ions attracted to cathode, gain electrons to form pure metal
  • Negative non-metal ions attracted to anode, lose electrons to form pure non-metal
• Electrolysis of aqueous solutions

  • Ions are free to move
  • Water can also undergo ionisation and affect the products
• Electrolysis of aluminium oxide

  1. Aluminium oxide mixed with cryolite to lower melting point

  2. Molten mixture undergoes electrolysis

  3. Aluminium formed at cathode, oxygen formed at anode
• Graphite anode in aluminium electrolysis reacts with oxygen to form carbon dioxide and wears away, needing replacement
• Electrolysis can be used to extract metals from their ionic compounds if the metal is more reactive than carbon
• Products of electrolysis of aqueous sodium chloride

  • Chlorine gas
  • Hydrogen gas
  • Sodium hydroxide solution
• Testing for products of electrolysis

  1. Hydrogen gas: collect in test tube, insert glowing splint (squeaky pop)

  2. Chlorine gas: collect in test tube, insert damp litmus paper (bleaches white)

  3. Sodium hydroxide: use universal indicator (turns purple)