Electrolysis

• Electrolysis

  Chemical breakdown of a compound into new substances using electrical energy
• Electrolysis process


  1. From a direct current (d.c.) power source

  2. Positive electrode (anode)

  3. Negative electrode (cathode)

  4. Ions migrate (move) to electrode of opposite charge when voltage applied

  5. Only one type of ion discharges (reacts) at each electrode
• Electrolyte


  • All ions of same charge migrate to oppositely charged electrode
  • Needs to be either molten or dissolved in water
  • Contains H2O / H+ / OH- ions
• Anode

  Positively charged electrode
• Cathode

  Negatively charged electrode
• Electrode

  Rod made of a metal or graphite that carries the current into or out of the electrolyte
• Reactions at the electrodes

  1. Anode: Oxidation - negative ions lose electrons

  2. Cathode: Reduction - positive ions gain electrons
• Oxidation occurs at the anode, reduction occurs at the cathode
• If ions gain electrons, they become reduced. If ions lose electrons, they become oxidised.
• Oxidation and reduction half-equations

  • 2Cl- → Cl2 + 2e-
  • 2H+ + 2e- → H2
• Metal ions become metal atoms, non-metal ions become non-metal molecules
• Reactivity series

  • Group 1/2/3 metals - more easily oxidised, more readily lose electrons
  • Hydrogen
  • Other metals - less reactive, less readily lose electrons
• Ions show opposite trend in reactivity series - more reactive ions higher up the series
• Electrolysis of molten lead bromide

  1. Cathode: Pb2+ + 2e- → Pb (silvery liquid)

  2. Anode: 2Br- → Br2 (brown gas)
• Adding a bulb to the circuit will light up as the electrolyte is electrolysed
• Electrolytes are substances that conduct electricity when dissolved or molten.
• The electrodes used in an electrochemical cell must be made from metals with different reduction potentials to ensure the flow of current.
• In electrolysis, the cathode attracts positively charged particles while the anode repels them.
• In an electrochemical cell, the metal with the lower reduction potential acts as the cathode and gains electrons, while the metal with the higher reduction potential acts as the anode and loses electrons.
• During this process, the metal at the anode undergoes oxidation by losing electrons, forming positive ions which then move through the electrolyte towards the cathode.
• This movement of ions creates a current flowing between the two electrodes.
• If the electrode is not removed, it will eventually become completely covered in the deposited material.
• Electroplating involves using direct current (DC) to deposit one metal onto another.
• During electrolysis, hydrogen gas forms at the negative electrode (cathode), while oxygen gas forms at the positive electrode (anode).
• The process of separating elements by using electrical energy is called electrolysis.
• Anode: The electrode where oxidation occurs
• The metal being plated is called the substrate or base metal, while the metal being deposited is called the coating metal.
• Anode: The electrode where oxidation occurs; the metal being plated