C3.4 Electrolysis

• What is electrolysis?

  Electrolysis is a chemical process that uses electricity to break down compounds.
• What happens at the anode during electrolysis?

  Oxidation occurs at the anode, where electrons are removed from the substance.
• What happens at the cathode during electrolysis?

  Reduction occurs at the cathode, where electrons are gained by the substance.
• What are the products of electrolysis of molten salts?

  • Cations migrate to the cathode and gain electrons.
  • Anions migrate to the anode and lose electrons.
• What is the significance of inert electrodes in electrolysis?


  Inert electrodes do not participate in the chemical reaction and only conduct electricity.
• Why is the amount of hydrogen produced during the electrolysis of water double that of oxygen?

  Because two hydrogen ions are produced for every one oxygen molecule during the reaction.
• What is the overall equation for the electrolysis of water?

  • 2H₂O(l) → 2H₂(g) + O₂(g)
• What is electroplating?

  Electroplating is a process that uses electrolysis to deposit a layer of metal onto a surface.
• How does electroplating work?

  During electroplating, metal ions in a solution are reduced at the cathode to form a metal layer.
• What happens to the metal at the anode during electroplating?

  The metal at the anode dissolves into the solution as metal ions.
• What are some applications of electroplating?

  • Coating objects to prevent corrosion
  • Enhancing appearance through decorative finishes
  • Improving electrical conductivity
• Why might copper be used in electroplating?

  Copper is used because it has good electrical conductivity and can provide a smooth finish.
• What is the role of the cathode in electroplating?

  The cathode is where the metal ions are reduced and deposited as a solid layer.
• What does reduction involve in terms of electrons?

  Gain of electrons
• What is the half equation for copper ions gaining electrons?

  Cu²+ + 2e⁻ → Cu
• What happens to magnesium in the half equation?

  Mg → Mg²+ + 2e⁻
• What does the term 'reduced' mean in the context of copper ions?

  Copper ions gain two electrons
• What is electrolysis?

  • Breaking down a substance using electricity
  • Involves oxidation and reduction reactions
• What is passed through an electrolyte during electrolysis?

  An electric current
• What happens to cations during electrolysis?

  They move towards the cathode and are reduced
• What happens to anions during electrolysis?

  They move towards the anode and are oxidised
• What do ions form when they gain or lose electrons during electrolysis?

  Uncharged substances
• What components make up an electrochemical cell?

  Anode, cathode, electrolyte, power source, wires
• What is produced at the anode during the electrolysis of molten lead bromide?

  Bromine gas
• What is produced at the cathode during the electrolysis of molten lead bromide?

  Lead metal
• What is the half equation for the cathode reaction in molten magnesium chloride?

  Mg²+ + 2e⁻ → Mg
• What is the half equation for the anode reaction in molten magnesium chloride?

  Cl₂ → 2Cl⁻ + 2e⁻
• What additional ions are present in aqueous solutions during electrolysis?

  Hydrogen ions (H⁺) and hydroxide ions (OH⁻)
• What is produced at the cathode if hydrogen ions and metal ions are present?

  Hydrogen gas if metal is more reactive
• What is produced at the anode if halide ions are present?

  Molecules of chlorine, bromine, or iodine
• What happens if no halide ions are present at the anode?

  Oxygen is formed from hydroxide ions
• What gas is produced at the cathode during the electrolysis of sodium chloride?

  Hydrogen gas
• What gas is produced at the anode during the electrolysis of sodium chloride?

  Chlorine gas
• How can you test for chlorine gas in the lab?

  It bleaches damp litmus paper white
• How can you test for hydrogen gas in the lab?

  It makes a “pop” sound when burnt
• What happens to the mass of the anode during electrolysis with copper electrodes?

  The mass of the anode decreases
• What happens to the mass of the cathode during electrolysis with copper electrodes?

  The mass of the cathode increases
• What should you do before weighing electrodes after an electrolysis experiment?

  Dry the electrodes to remove solution
• What is the half equation for the anode reaction in copper sulfate electrolysis?

  4OH⁻ → 2H₂O + O₂ + 4e⁻
• What is the role of the electrical supply in electrolysis?

  It pulls electrons off atoms at the anode