Electroplating – IGCSE Chemistry Definition

Electroplating uses electrolysis to deposit a thin layer of one metal onto the surface of another object. The 0620 syllabus requires you to describe the setup, choose the correct electrode connections, and explain why electroplating is useful. This is a practical application of electrolysis that examiners test on Papers 2 and 4.

The 0620 definition

Electroplating is the process of coating a metal object with a thin layer of another metal by electrolysis.

The setup

Component	What it is
Cathode (negative electrode)	The object to be plated
Anode (positive electrode)	A piece of the plating metal
Electrolyte	A solution containing ions of the plating metal

How it works

1. The plating metal anode dissolves: metal atoms lose electrons and enter the solution as ions (oxidation)

   e.g. Ag → Ag⁺ + e⁻

2. The plating metal ions in solution migrate to the cathode (the object)

3. At the cathode, the metal ions gain electrons and are deposited as a thin, even layer (reduction)

   e.g. Ag⁺ + e⁻ → Ag

The anode gradually gets smaller and the cathode gains a layer of plating metal. The concentration of the solution stays approximately constant because the anode replaces the ions that are deposited.

Example: silver plating a spoon

• Cathode: the steel spoon (object to be plated)
• Anode: a piece of pure silver
• Electrolyte: silver nitrate solution (contains Ag⁺ ions)

Reasons for electroplating

Reason	Example
Prevent corrosion / rust	Chromium plating on steel car parts
Improve appearance	Gold or silver plating on jewellery
Reduce cost	Coating a cheap metal with an expensive one
Improve hardness / durability	Nickel plating on tools

Worked exam question

Describe how you would electroplate a steel key with copper. State the cathode, the anode, and the electrolyte, and explain why the copper anode gets smaller during the process. (4)

Mark scheme

Cathode: the steel key [1]; anode: a piece of copper [1]; electrolyte: copper(II) sulfate solution (or any solution containing Cu²⁺ ions) [1]; the copper anode dissolves because copper atoms lose electrons and enter the solution as Cu²⁺ ions / oxidation occurs at the anode [1]

Common exam mistakes

• Putting the object at the anode instead of the cathode. The object to be plated must be the cathode — metal ions are deposited by reduction at the cathode.
• Choosing the wrong electrolyte. The electrolyte must contain ions of the plating metal. To plate with silver, use a silver salt solution, not a copper salt.
• Forgetting to explain why the anode dissolves. The anode is made of the plating metal and undergoes oxidation — its atoms lose electrons and enter the solution as ions.