(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.