ELECTROLYSIS

• Electrolysis

  The process of using electricity to drive a chemical reaction
• Electrolysis of aqueous solutions

  • Need to consider the ions present in water (H+ and OH-)
  • Need to consider the reactivity series to determine which ions will be reduced at the cathode
• Electrolysis of copper sulfate solution

  1. Copper ions (Cu2+) are reduced at the cathode to form copper atoms

  2. Oxygen gas is produced at the anode from the oxidation of hydroxide ions
• Inert electrodes

  Electrodes that do not react with the chemicals being produced during electrolysis (e.g. platinum)
• Electrolysis of aqueous solutions often produces oxygen gas at the anode
• Aqueous


  Dissolved in water
• Water molecules splitting

  1. Produce hydrogen ion H+

  2. Produce hydroxide ion OH-
• Sodium chloride

  Has sodium ion Na+ and chloride ion Cl-
• Electrolysis of sodium chloride solution

  1. Ions attracted to cathode: sodium ion Na+ and hydrogen ion H+

  2. Ions attracted to anode: chloride ion Cl- and hydroxide ion OH-
• Reactivity series

  • Sodium more reactive than hydrogen
• Hydrogen gas produced at cathode
• Chlorine gas produced at anode
• If aqueous solution contains halide ions, the halogen will be produced at the anode
• Reaction at cathode


  1. Hydrogen ion gains 1 electron to form hydrogen atom

  2. Hydrogen atoms pair to form hydrogen molecule H2
• Reaction at anode

  1. Chloride ion loses 1 electron to form chlorine atom

  2. Chlorine atoms pair to form chlorine molecule Cl2
• Half equations can be written to show reactions at cathode and anode