Chemical Changes

• Electrolysis

  Splitting up with electricity
• Electrolysis process

  1. Place electrolyte in beaker

  2. Use electrodes (anode and cathode)

  3. Connect electrodes with wire

  4. Add power supply (e.g. battery)

  5. Electric current passes through electrolyte
• Electrolyte

  Liquid or solution containing an ionic compound with free-moving ions
• Electrolytes

  • Aqueous copper sulfate
  • Molten lead bromide
• Electrodes

  • Solid conductors, generally made of metal or carbon
  • Anode (positive electrode)
  • Cathode (negative electrode)
• Negative bromide ions

  Attracted to positive anode, discharged to form bromine gas
• Positive lead ions

  Attracted to negative cathode, discharged to form pure lead
• Oxidation and reduction at electrodes

  1. At anode: Bromide ions oxidized, lose 1 electron (half equation)

  2. At cathode: Lead ions reduced, gain 2 electrons
• Overall, electrons transferred from negative ions to positive ions using electricity to convert ions to pure elemental forms
• Extracting reactive metals from their oxides

  1. Melt the oxides into their molten ionic compounds

  2. Reduce the metal in the oxide to remove the oxygen
• Metals less reactive than carbon

  Can be reduced with carbon
• Metals more reactive than carbon

  Require electrolysis to extract
• Electrolysis

  • Separates ionic compounds into their pure elements by passing an electric current through an electrolyte
  • Requires the ions to be able to move freely
• Extracting aluminium from bauxite

  1. Purify aluminium oxide from bauxite

  2. Mix aluminium oxide with cryolite to lower melting point

  3. Melt the mixture
• Electrolysis of molten aluminium oxide

  1. Use a beaker to hold the molten electrolyte

  2. Use a positive carbon anode and negative carbon cathode

  3. Connect the electrodes with a wire and power source
• Reactions at the electrodes

  1. At the anode, oxygen 2- ions form oxygen gas and release electrons

  2. At the cathode, aluminium 3+ ions gain 3 electrons to form molten aluminium metal
• Oxidation

  Loss of electrons
• Reduction

  Gain of electrons
• Reactivity series of metals


  Order of how easily metals form positive ions
• Metals


  • Have electrons in the outermost shell that they want to get rid of
  • Form positive ions when they react
• Metals included in reactivity series

  • Group 1 metals
  • Group 2 metals
  • Transition metals
  • Carbon
  • Hydrogen
• Determining reactivity series


  1. React each metal with acid or water

  2. Compare reaction speed and violence

  3. Measure temperature change
• Fair test for comparing reactivity


  • Use same mass and surface area of metal samples
  • Use same type and concentration of acid
• Reaction of metals with water

  1. Form metal hydroxides and hydrogen

  2. Only most reactive metals react with water
• More reactive metal


  Can displace less reactive metal in a solution
• Magnesium can displace iron in iron sulfate solution, but copper cannot displace iron in iron sulfate solution