Electrolysis

Electrolysis

1. Splitting ionic compounds into constituent elements

2. Electrolyte

   • Ionic compounds that dissolve in water
   • A solution/liquid that conducts electricity

3. Electrodes

   • Cathode attracts positive ions
   • Anode attracts negative ions
   • When a voltage is applied, charged ions are attracted to opposite electrodes

4. OILRIG

   • Oxidation Is Loss
   • Reduction Is Gain

5. Half equations

   • Show electron transfer
   • Oxidation
     • Na -> Na+ + e-
     • Sodium becomes sodium ion
   • Reduction
     • 2H+ + 2e- -> H2

6. Electrochemical Cells

   • Solution Electrolyte
     • Two inert electrodes
       • Graphite
       • Platinum
     • Clean surfaces using emery paper
     • Place electrodes into a beaker of electrolyte
     • Connect to power supply
     • Products include hydrogen and hydroxide ions
       • Cathode
         • Hydrogen and metal ions present
           • Metal more reactive than hydrogen
             • Hydrogen produced
           • Metal less reactive than hydrogen
             • Pure metal produced
       • Anode
         • Hydroxide and halide ions present
           • Halide produced
         • if halide ions not present
           • Oxygen produced
   • Molten Ionic Electrolyte
     • Heat solid ionic substance in crucible until molten
       • Solid can't be electrolysed - no free ions
     • Dip in inert electrodes
     • Connect to power supply

7. Extraction of metals

   • Examples
     • Dilute sulfuric acid
       • Anode
         • Oxygen
           • Glowing splint relights
       • Cathode
         • Hydrogen
           • Lit splint -> squeaky pop
     • Sodium Sulfate
       • Cathode
         • Hydrogen
           • Lit splint -> squeaky pop
       • Anode
         • Oxygen
           • Glowing splint relights
     • Concentrated aqueous sodium chloride
       • Cathode
         • Hydrogen gas
           • Lit splint -> squeaky pop
       • Anode
         • Chlorine gas
           • Moist litmus paper -> bleached
     • Copper chloride solution
       • Cathode
         • Copper
       • Anode
         • Chlorine gas
     • Molten lead (II)
       • Cathode
         • Lead
           • Shiny metal
       • Anode
         • Bromine
           • Brown gas

8. Requires energy

   • Higher current = faster rate of electrolysis

9. Copper Sulfate

   • Inert electrodes
     • Cathode
       • Copper
     • Anode
       • Oxygen
       • Water
   • Non-Inert electrodes (Copper)
     • Mass of cathode = increase
       • Copper transferred from anode to cathode
     • Mass of anode = decrease