Electroplating
Definition and meaning of Electroplating in chemistry.
Electroplating is a process in which an electric current is used to deposit a thin layer of metal onto the surface of a conductive object from a solution of metal ions.
In more detail
The object to be plated is made the cathode of an electrolytic cell, while a bar of the plating metal (or an inert conductor) serves as the anode, both immersed in an electrolyte containing dissolved ions of the plating metal. When current flows, metal cations in solution are reduced and deposited as solid metal atoms onto the cathode's surface, while at a reactive anode, metal atoms are oxidized into solution to replenish the ion supply. The thickness and quality of the coating depend on current density, plating time, electrolyte composition, and temperature. Electroplating is used industrially to improve corrosion resistance, wear resistance, electrical conductivity, or appearance of metal objects.
Key facts
| Field | Physical Chemistry |
|---|---|
| Cathode reaction | M^n+ + n e- → M(s) |
| Common electrolyte example | CuSO4(aq) |
| Current type used | Direct current (DC) |
Electroplating copper onto a metal spoon: the spoon is connected as the cathode and a copper bar as the anode, both dipped in copper(II) sulfate solution. Passing a direct current reduces Cu2+ ions at the spoon's surface (Cu2+ + 2e- to Cu), depositing a shiny copper coating, while the copper anode dissolves (Cu to Cu2+ + 2e-) to maintain the ion concentration.
Frequently asked questions
Why is the object being plated made the cathode?
Reduction occurs at the cathode, and depositing metal requires reducing dissolved metal cations into neutral metal atoms, so the object must be the electrode where reduction takes place.
What happens if an inert anode is used instead of a reactive metal anode?
With an inert anode (such as platinum), metal ions in solution are not replenished, so the electrolyte's metal ion concentration gradually decreases as plating proceeds.