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3.2.5Atomic Structure and the Periodic Table

Extracting Copper

5 min read 5 parts Lesson 1 of 10 Unit quiz

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Section 1 of 5Purifying Copper by Electrolysis

3.2.5 Extracting Copper

Electrolysis separates pure copper from its impurities, using the impure metal as the anode.

Anode
  • The impure copper is the anode, and copper atoms lose electrons and dissolve as Cu²⁺ ions: Cu → Cu²⁺ + 2e⁻.
Cathode
  • A thin sheet of pure copper is the cathode, where Cu²⁺ ions gain electrons to form pure copper: Cu²⁺ + 2e⁻ → Cu.
Electrolyte
  • The electrolyte is an aqueous solution of a soluble copper salt, such as copper(II) sulfate.
Sludge
  • Impurities that do not dissolve fall to the bottom of the cell as anode sludge, which may contain valuable metals such as silver.

Section 2 of 5Electrolysis With Graphite and Copper Electrodes

The electrode material decides which products form during electrolysis of copper(II) sulfate.

1
With graphite electrodes, electrolysis of aqueous copper(II) sulfate produces oxygen at the anode and copper at the cathode.
2
With copper electrodes, the anode gradually becomes thinner as copper atoms leave it, while the cathode gradually becomes thicker.
3
The blue colour of the solution stays constant, because copper ions leave the solution at the same rate that they enter it.

Section 3 of 5Obtaining Copper by Displacement

Obtaining Copper by Displacement
Scrap iron
  • Scrap iron can be used to displace copper from solutions such as copper(II) sulfate.
Equation
  • Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s), with iron more reactive than copper.
Ionic form
  • Fe(s) + Cu²⁺(aq) → Fe²⁺(aq) + Cu(s), with sulfate ions as spectator ions.
Advantage
  • This method reuses scrap iron that might otherwise be sent to landfill.

Section 4 of 5Worked Example

Question Explain why the blue colour of copper(II) sulfate solution stays the same during electrolysis with copper electrodes.

  1. At the cathode, Cu²⁺(aq) + 2e⁻ → Cu(s) removes copper ions from the solution.
  2. At the anode, Cu(s) → Cu²⁺(aq) + 2e⁻ adds copper ions to the solution.
  3. The copper ions leave and enter the solution at the same rate, so their concentration does not change.

Answer Because copper ions are removed and replaced at equal rates, the concentration and blue colour of the solution remain constant.

Section 5 of 5Exam Checklist & Tips

3.2.5 – Key Points for the Exam

  • Electrolytic purification Using electrolysis with the impure metal as the anode to produce a pure metal at the cathode.
  • Anode sludge Insoluble impurities that collect below the anode during purification.
  • Electrolyte A liquid containing ions that conducts electricity during electrolysis.
  • Half-equation An equation showing the electrons gained or lost at one electrode.

Common Mistakes

  • Placing impure copper at the cathode; the impure metal is always the anode.
  • Saying the anode gains mass; it loses mass as copper atoms dissolve.
  • Writing copper ions as Cu⁺ instead of Cu²⁺.
  • Forgetting that impurities such as silver collect as sludge rather than dissolving in the electrolyte.
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