SC10

• Electrolysis - the breaking down of a substance using electricity

  An electric current is passed through an electrolyte (a molten/dissolved ionic compound) causing it to decompose
• As ions are reduced or oxidised, they form uncharged substances and are discharged from the electrolyte:

  • Cations (positive ions) move towards the cathode (negative electrode) and are reduced (gain electrons)
  • Anions (negative ions) move towards the anode (positive electrode) and are oxidised (lose electrons)
• Molten Ionic Compounds:

  • ions move freely and conduct electricity
• Aqueous Solutions:

  • hydrogen and hydroxide ions present
  • hydrogen gas produced at the cathode if metal ions are more reactive (sodium < hydrogen < silver)
  • oxygen is formed at the anode unless there are halide ions present (positive ion < oxygen < halide)
• Copper Sulfate with Inert Electrodes:

  • four different ions (Cu+2, SO4-2, H+, OH-)
  • copper is less reactive than hydrogen so copper metal is produced at the cathode - see brown coating
  • no halide ions so water and oxygen produced at the anode - see bubbles of gas forming
• Non-Inert Electrodes:

  • copper electrodes used
  • mass of anode decreases and mass of cathode increases
  • measure electrode masses before and after electrolysis - dry electrodes before weighing
  • increasing current will increase the rate of electrolysis so there is a bigger mass difference
  • impurities from an impure copper anode will sink down as sludge