ElectroplatingOxford AQA IGCSE Chemistry: Revision notes

Electroplating is the use of electrolysis to coat the surface of one metal object with a thin layer of another metal. A current is passed through an electrolyte containing ions of the coating metal, causing that metal to be deposited onto the object being plated.

Objects are electroplated for three main reasons:

• Appearance — giving a cheaper metal object an attractive, shiny coating (e.g. gold- or silver-plated jewellery)
• Durability — adding a harder-wearing surface layer
• Prevention of corrosion — coating a reactive metal with one that resists rusting or corrosion, protecting the object underneath

In electroplating, the object to be coated is made the cathode (negative electrode), and a bar of the pure coating metal is made the anode (positive electrode). The electrolyte is a solution containing ions of the coating metal.

As current flows, metal ions from the electrolyte are discharged and deposited onto the object at the cathode, while the anode dissolves to replace the metal ions lost from the solution — keeping the concentration of the electrolyte roughly constant.

Two examples commonly referenced:

• Copper plating — depositing a layer of copper onto an object, often used in electronics and before further plating with other metals
• Silver plating — coating cheaper metal cutlery or jewellery with a layer of silver, for appearance and to reduce cost compared with solid silver