Lecture on Electrolysis

Introduction to Electrolysis

• Electrolysis involves using electricity to cause a chemical reaction.
• Requires a DC power supply connected to two electrodes.
• Electrodes are typically graphite (carbon) or metal.
• Electrodes are inserted into an electrolyte (solution with an ionic compound).

Key Terms

• Cathode: Negative electrode; connected to the negative terminal.
• Anode: Positive electrode; connected to the positive terminal.
• Electricity Flow: Charge flow, not just electrons.
• Ions in Solution: Free to move, facilitating electricity flow.

Electrode and Electrolyte Interaction

• Reaction depends on electrode material and electrolyte type.
• Carbon Electrodes: Inert, do not react during the process.
• Example Electrolyte: Sodium chloride solution.

Dissociation and Ions

• Ionic compounds partially dissociate in solution.
• Example Ions in Solution: Na⁺, Cl⁻, H⁺, OH⁻.

Principles of Charge

• Cations: Positive ions, attracted to the cathode.
  • Example: Na⁺, H⁺.
• Anions: Negative ions, attracted to the anode.
  • Example: Cl⁻.

Reduction and Oxidation

• Cations gain electrons and are reduced at the cathode.
• Anions give electrons and are oxidized at the anode.
• OIL RIG Mnemonic: Oxidation Is Loss, Reduction Is Gain.

Reactivity and Product Formation

• Rule for Cathode: Less reactive cation is reduced.
  • If metal cation is more reactive than hydrogen, hydrogen is produced.
• Rule for Anode: Halide anions are oxidized; otherwise, oxygen is produced.

Example Reactions

• Sodium Chloride Solution:
  • Hydrogen gas produced at cathode.
  • Chlorine gas produced at anode.
• Copper Sulfate Solution:
  • Copper deposited at cathode.
  • Oxygen gas produced at anode.

Electrolysis of Water and Molten Compounds

• Water Electrolysis: Produces hydrogen and oxygen gases.
• Molten Compounds: Ions are free to move without water.
  • Example: Aluminium from aluminium oxide.

Energy Considerations

• High energy needed to melt compounds.
• Cryolite: Lowers melting point for aluminum extraction.

Purifying Metals

• Copper Purification:
  • Impure copper as anode, pure copper as cathode.
  • Copper ions reduced at cathode, impurities remain solid.

Conclusion

• Electrolysis is versatile for chemical reaction manipulation and material purification.