(17) Electrolysis of copper sulfate CuSO4 (aq) using graphite and copper electrodes - GCSE Chemistry

Overview of Electrolysis of Aqueous Copper Sulfate

  • Objective: Understand the electrolysis process of aqueous copper sulfate and its application in copper refining.

Electrolysis Setup

  • Electrolyte: Aqueous copper sulfate solution containing:

    • Copper (II) ions (Cu²⁺)

    • Sulfate ions (SO₄²⁻)

    • Hydrogen ions (H⁺)

    • Hydroxide ions (OH⁻)

  • Electrodes: Using graphite electrodes which are inert and do not participate in the reaction.

Reactions at the Electrodes

At the Cathode

  • Discharge Reactions:

    • Cu²⁺ ions and H⁺ ions are attracted to the cathode.

    • Priority of Discharge: Cu²⁺ is less reactive than H⁺, hence:

      • Cu²⁺ ions are reduced to copper metal (Cu) by gaining two electrons:

      • Reaction: Cu²⁺ + 2e⁻ → Cu (s)

At the Anode

  • Discharge Reactions:

    • SO₄²⁻ and OH⁻ ions are attracted to the anode.

    • Priority of Discharge: The sulfate does not discharge; therefore, OH⁻ discharges to produce water and oxygen:

      • Reaction: 4OH⁻ → 2H₂O + O₂ + 4e⁻

Using Copper Electrodes

  • Electrolyte remains the same, but electrodes are now copper instead of graphite.

At the Cathode

  • Cu²⁺ and H⁺ again are present:

    • Cu²⁺ ions are still reduced to copper metal (Cu), causing the cathode to increase in size as it gets coated with copper.

At the Anode

  • Oxidation processes include:

    • Cu can oxidize more readily than SO₄²⁻ or OH⁻:

      • Reaction: Cu (s) → Cu²⁺ + 2e⁻

  • As a result, copper metal from anode turns into Cu²⁺ ions, adding copper to the electrolysis solution.

Application in Copper Refining

  • Understanding the Process:

    • Anode: Copper ore (contains copper) undergoing oxidation.

    • Cathode: Thin strip of pure copper, facilitating purification.

  • Chemical Reactions:

    • At the cathode: Cu²⁺ ions reduce to form pure copper:

      • Reaction: Cu²⁺ + 2e⁻ → Cu (s)

    • At the anode: Copper from ore oxidizes to Cu²⁺ ions while remaining impurities (sand, etc.) settle at the bottom.

  • Outcome:

    • Constant increase in the size of the pure copper cathode as copper ions deposit, while the copper ore anode diminishes.

    • Resulting in pure copper metal collected at the cathode and impurities collected as sludge at the bottom.

Conclusion

  • This process of electrolysis allows for efficient purification of copper, transforming a rock containing copper into pure copper metal.