Chemistry

• Electrolysis


  The process of breaking down an ionic substance into its elements by passing an electric current through it
• The process of electrolysis


  1. Ionic substance is melted or dissolved

  2. Ions are free to move about

  3. Current is passed through the molten or solution

  4. Substance is broken down into elements
• Cathode


  The negative electrode where positively charged ions move to
• Anode


  The positive electrode where negatively charged ions move to
• Electrolysis of molten ionic compounds


  1. Metal is produced at the cathode

  2. Non-metal is produced at the anode
• Electrolysis of molten ionic compounds


  • Metal is the positive ions
  • Non-metal is the negative ions
• Using electrolysis to extract metals


  1. Metals more reactive than carbon are extracted by electrolysis of molten compounds

  2. Large amounts of energy are used to melt the compounds and produce the electrical current

  3. Aluminium is manufactured by electrolysis of molten aluminium oxide and cryolite using carbon as the positive electrode
• Electrolysis of aqueous solutions


  • Ions discharged depend on the relative reactivity of the elements
  • Hydrogen is produced at the cathode unless the metal is less reactive than hydrogen
  • One of the halide ions is produced at the anode if present, otherwise oxygen is formed

  
• Representation of reactions at electrodes as half equations


  1. Negative electrode: X+ + e- -> X

  2. Positive electrode: X- -> e- + X
• The small number in a half equation is always the same as the 2 larger numbers within the equation
• Electrons are represented by the symbol 'e-' in half equations