Electrolysis Basics

What is Electrolysis?

• Electrolysis involves using electricity to cause a chemical reaction.
• Requires a DC power supply connected to two electrodes (graphite or metal) inserted into an electrolyte (ionic compound dissolved in water).
• Electrode connected to the negative terminal is the cathode, and the positive terminal is the anode.
  • Cathode: Negative electrode
  • Anode: Positive electrode
• Electrons flow in a complete circuit with ions free to move in the solution.

Understanding Electrolysis with Sodium Chloride Solution

• Electrodes: Carbon (inert, do not change/react)
• Electrolyte: Sodium chloride solution, dissociates into Na+ and Cl- ions.
• Water dissociates into H+ and OH- ions, free to move in the solution.

Charge Attraction

• Opposite charges attract:
  • Positive ions (cations, e.g., Na+ and H+) move to the cathode.
  • Negative ions (anions, e.g., Cl-) move to the anode.

Reactions at Electrodes

• Reduction at the cathode: Cations gain electrons to become neutral atoms.
  • Cations are always reduced at the cathode.
• Oxidation at the anode: Anions lose electrons which are accepted by the anode.
  • Anions are oxidized at the anode.

Rules for Electrolysis

At the Cathode

• Less reactive cation is reduced.
  • Hydrogen (less reactive than sodium) will be reduced over sodium in a sodium chloride solution.
• Half Equation for Reduction:
  • H+ + e- → H2

At the Anode

• If the anion is a halide (e.g., Cl-, Br-, I-), it gets oxidized.
  • Half Equation:
  • 2Cl- → Cl2 + 2e-
• Non-halide anions result in oxygen production.
  • Half Equation:
  • 4OH- → O2 + 2H2O + 4e-

Electrolysis of Copper Sulfate Solution

• Cations: Copper (Cu2+) is less reactive than hydrogen, so it is reduced at the cathode.
  • Result: Copper coating on the cathode.
• Anions: Oxygen is oxidized at the anode (no halide in solution).
• Solution: Results in sulfuric acid (H2SO4) formation in solution.

Electrolysis of Pure Water

• Produces hydrogen gas at the cathode and oxygen gas at the anode.
• Most common method for producing these gases.

Electrolysis with Molten Ionic Compounds

• Ions move freely in molten compounds, no water needed.
• Example: Aluminum extraction from aluminum oxide using molten compounds.
  • Cathode: Pure aluminum coats it.
  • Anode: Oxygen produced.
  • Requires a lot of energy; cryolite can lower melting point.

Purifying Metals via Electrolysis

• Used for purification of impure metals (e.g., copper).
• Impure copper as anode; pure copper as cathode; copper sulfate solution as electrolyte.
• Cathode mass increases as pure copper deposits.
• Impurities remain solid and sink to the bottom.

Conclusion

• Electrolysis is a versatile process for extracting and refining metals, producing gases, and more.
• Understanding the rules of reactivity and the process of oxidation/reduction is key.
• Watch related videos or tutorials for more examples and detailed explanations.