Electroplating (HL) (DP IB Chemistry): Revision Note

Electroplating

• Electroplating involves the electrolytic coating of an object with a very thin metallic layer

• This is done for:

  • Decoration, such as gold-plated jewellery

  • Corrosion prevention, such as zinc coated (galvanized) iron to resist rusting

How electroplating works

• Electroplating uses electrolysis with active electrodes

  • The metal is deposited onto the cathode (the object being plated)

• The anode is typically made of the same metal that is being deposited

  • This helps to:

    • Replenish metal ions in the electrolyte

    • Keep the metal ion concentration stable

• The rate of deposition must be carefully controlled to ensure a smooth, even coating

Example: silver plating a spoon

• A common electrolyte for silver plating is sodium silver cyanide, Na[Ag(CN)₂], also known as sodium dicyanoargentate(I)

• The anode is impure silver, which slowly dissolves during electrolysis:

  • At the anode (oxidation):

Ag (s) + 2CN^- (aq)  →  [Ag(CN)₂]^- (aq)+ e^-

• The cathode is the spoon, which receives the silver coating:

  • At the cathode (reduction):

[Ag(CN)₂]^- (aq) + e^-  →  Ag (s) + 2CN^- (aq) 

• The thickness of the metallic plating can be controlled by adjusting:

  • The electrical current

  • The time

  • The electrolyte concentration

Electroplating plastics

• Even non-conductive materials like plastics can be electroplated using a special process:

  • The surface is first etched or pitted

  • Metallic particles are embedded into the surface so it can conduct electricity

  • Once conductive, the plastic can be electroplated like a metal object