electrolysis of molten compounds

• • Binary ionic compounds consists of just two elements joined together by ionic bonding
  • When these compounds are heated beyond their melting point, they become molten and can conduct electricity as their ions can move freely and carry the charge
  • These compounds undergo electrolysis and decompose into their constituent elements
  • Lead(II) bromide is an ionic solid with a relatively low melting point and can be used to illustrate the electrolysis of a molten compound

  A) metallic

  B) bromine

  
• Method:

  1. Add PbBr2 into a crucible and heat so it melts, allowing ions to be free to move n conduct electric charge
  2. Add two graphite rods (electrodes), connect to battery
  3. Turn on battery -> electrolysis
  4. Negative bromide ions move to anode n lose two electrons -> bromine molecules.
  5. bubbling as brown bromine gas is given off
  6. Positive lead ions move to cathode n gain electrons -> grey lead metal which deposits on the bottom of the electrode

  Electrode Products:

  • Anode: Brown fumes of bromine gas
  • Cathode:A grey bead of molten lead is formed
• Predicting the Products

  • To predict the products of any binary molten compound first identify the ions present
  • The positive ion will migrate towards the cathode and the negative ion will migrate towards the anode
  • Therefore the cathode product will always be the metal and the product formed at the anode will always be the non-metal
  • For example, Zinc chloride will produce zinc at the cathode and chlorine at the anode