The Copper Factory ⚡🔵
Electrolysis of Copper(II) Sulfate — Graphite vs Copper Electrodes
🕵️ The Mystery of the Fading Blue
Imagine a glass tank full of brilliant blue copper(II) sulfate solution. You plunge in two electrodes and switch on the power. With graphite electrodes, something strange happens — the blue colour slowly drains away, like ink disappearing from water. With copper electrodes? The blue stays. One electrode visibly shrinks. The other grows. This is how industry purifies copper to 99.99% — the backbone of every electrical wire on Earth.
⬛ Graphite (Inert) Electrodes
Cathode (–) — Reduction
Cu²⁺ ions migrate to the negative electrode, gain electrons, and are reduced to solid copper. A pink/brown layer builds up.
Anode (+) — Oxidation
OH⁻ from water is preferentially discharged over SO₄²⁻. Oxygen bubbles form. The graphite anode is unchanged.
🔵 Solution Observation
Cu²⁺ is being removed at the cathode but NOT replaced. The blue colour fades to colourless/pale blue.
🏭 Copper Purification Factory
(Scenario B only)Real-world copper ore contains silver, gold, and zinc impurities. Electrolysis separates them with atomic precision.
⬛ Graphite — Half Equations
🟠 Copper — Half Equations
⚠️ Examiner's Traps
"The solution fades because the electrodes absorb the colour" — WRONG. It fades because Cu²⁺ ions are being removed by reduction at the cathode.
"With copper electrodes, the anode gains mass" — WRONG. The cathode gains mass; the anode loses mass.
"SO₄²⁻ is discharged at the anode with graphite" — WRONG. OH⁻ is preferentially discharged; O₂ forms.
With copper electrodes: mass gained at cathode = mass lost at anode. The overall concentration of Cu²⁺ stays constant.
The pink/brown deposit at the cathode is copper, not rust. Always describe it as "pink" or "brown solid".
📚 Mark-Earning Keywords
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