Purifying copper
Copper from a furnace is not quite pure. One more step makes it purer. That step is called electrolytic refining.
- A beaker holds copper sulphate solution. A pure strip and an impure bar stand in it.
- A battery joins them. The impure bar is on the plus side.
- Copper leaves the impure bar as ions.
- The ions travel to the strip and build up as pure copper.
- Bits that do not dissolve fall to the bottom as anode mud.
The rule
An electrode is a bar or strip in the solution. Current enters or leaves the solution there.
Electrolytic refining makes pure copper from impure copper. The impure copper is the anode. The cathode is a thin strip of pure copper. The solution is copper sulphate with a little acid.
The anode is the plus electrode. The cathode is the minus electrode. The electrolyte is the solution that carries the current.
| Part | What it is | What happens there |
|---|---|---|
| Anode (+) | Impure copper | Copper dissolves: Cu → Cu²⁺ + 2e⁻ |
| Cathode (−) | Thin strip of pure copper | Copper builds up: Cu²⁺ + 2e⁻ → Cu |
| Electrolyte | Copper sulphate solution with a little acid | The ions carry the current |
Here e⁻ means an electron. Cu²⁺ is a copper atom that has lost two electrons.
The Cu²⁺ ions are positive. So they travel to the minus cathode.
Some impurities dissolve and stay in the solution. Others do not dissolve. These fall under the anode as anode mud.
The same plan refines other metals. The impure metal is the anode. A thin strip of the pure metal is the cathode. The electrolyte holds a salt of that metal.
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