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4.2.1Electrochemistry

Electroplating — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 20 of 20 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Part 1 of 5The Electroplating Cell

4.2.1 Electroplating

Copper plating an iron key is a typical example, using copper(II) sulfate solution.

Cathode
  • The object to be plated is made the cathode, which is the negative electrode connected to the negative terminal of the supply.
Anode
  • The anode is a piece of the pure plating metal and is connected to the positive terminal.
Electrolyte
  • The electrolyte is an aqueous solution of a soluble salt containing ions of the plating metal.
Direct current
  • A direct current is passed through the circuit so that metal ions are attracted to the cathode.
PartMaterial for copper plating
Cathode (negative)Object to be plated
Anode (positive)Pure copper
ElectrolyteAqueous copper(II) sulfate

Part 2 of 5What Happens at the Electrodes

1
At the anode, copper atoms lose electrons and dissolve into the solution as copper(II) ions: Cu(s) → Cu²⁺(aq) + 2e⁻.
2
This loss of electrons is oxidation, and it makes the anode slowly get smaller.
3
Copper(II) ions in the solution move to the cathode, which is the negative electrode.
4
At the cathode the ions gain electrons and form copper atoms: Cu²⁺(aq) + 2e⁻ → Cu(s).
5
This gain of electrons is reduction, and the copper atoms build up as a thin layer on the object.

Part 3 of 5Why Objects Are Plated

Why Objects Are Plated
Corrosion resistance
  • A coating such as chromium or nickel keeps air and water away from the metal underneath, so it does not rust or corrode.
Appearance
  • Silver plating on cutlery or jewellery gives a shiny, attractive surface that is cheaper than making the whole object from silver.
Zinc coating
  • Steel can be coated with zinc, which is called galvanising, to protect it from rusting.
Cost saving
  • A thin layer of an expensive metal on a cheap metal gives the benefits of the surface metal at lower cost.

Part 4 of 5Controlling the Result

Electrolyte stays constant
  • Copper ions removed at the cathode are replaced from the anode, so the blue colour of the solution stays the same.
Mass changes
  • The cathode gains mass and the anode loses mass, by about the same amount.
Clean surface
  • The object must first be cleaned of grease so that the metal layer sticks firmly.
Different plating metals
  • Silver plating uses a silver anode and silver nitrate solution, and tin plating uses a tin anode with a tin salt solution.

Part 5 of 5Exam Checklist & Tips

4.2.1 – Key Points for the Exam

  • Electroplating Coating an object with a thin layer of metal using electrolysis.
  • Cathode The negative electrode where reduction takes place.
  • Anode The positive electrode where oxidation takes place.
  • Electrolyte A liquid or solution containing ions that conducts electricity and is broken down.
  • Galvanising Coating iron or steel with zinc to prevent rusting.

Common Mistakes

  • Making the object to be plated the anode instead of the cathode.
  • Using an unrelated metal salt as the electrolyte rather than a salt of the plating metal.
  • Writing the electrode equations the wrong way round or leaving out the electrons.
  • Saying the electrolyte becomes paler; in copper plating the concentration stays almost the same.

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