Electrolysis Lecture Notes

Definition of Electrolysis

• Electrolysis is a process where electricity is used to induce a chemical change that would not occur spontaneously.
• Often used to decompose compounds into their elemental components.

Examples of Electrolysis

1. Sodium Chloride (NaCl) Electrolysis

   • Breaks down into sodium metal (Na) and chlorine gas (Cl₂).
   • Involves oxidation-reduction reaction (Redox).
   • Oxidation Numbers:
     • Na: +1 → 0 (Reduction, gains electrons)
     • Cl: -1 → 0 (Oxidation, loses electrons)
   • Requires electrical energy as NaCl is stable and non-spontaneous.
   • Mechanism:
     • Battery has a positive side (pulls electrons) and a negative side (pushes electrons).
     • Electrodes: Anode (site of oxidation) and Cathode (site of reduction).
     • Requires molten NaCl at high temperature (~1500°F or 800°C).
     • Chemical Equation:
       • Unbalanced: NaCl → Na + Cl₂
       • Final balanced equation with physical states: 2 Na(l) + Cl₂(g)

2. Water (H₂O) Electrolysis

   • Decomposes into hydrogen gas (H₂) and oxygen gas (O₂).
   • Also involves a Redox reaction.
   • Oxidation Numbers:
     • H: +1 → 0 (Reduction, gains electrons)
     • O: -2 → 0 (Oxidation, loses electrons)
   • Non-spontaneous, requires added electrolyte (e.g., sulfuric acid) for conductivity.
   • Mechanism:
     • Uses an electrolytic cell with test tubes to collect gases.
     • Hydrogen gas forms at the cathode; Oxygen forms at the anode.
     • Chemical Equation:
       • Balanced: 2 H₂O → 2 H₂ + O₂
       • Ratio of H₂:O₂ is 2:1, hence twice as much hydrogen gas produced.

Components of Electrolytic Cell

• Electrodes:
  • Anode: Site of oxidation, connected to positive battery terminal.
  • Cathode: Site of reduction, connected to negative battery terminal.
• Battery: Supplies the electrical energy needed.
• Electrolyte: Substance that allows electricity to flow (e.g., molten NaCl, H₂SO₄ in water).

Importance of Electrolysis

• Enables non-spontaneous reactions to occur using electrical energy.
• Allows separation and extraction of elements like sodium, chlorine, hydrogen, and oxygen.