Electroplating Applications

Electroplating is tested in the Cambridge 0620 syllabus as a practical application of electrolysis. Questions typically ask candidates to identify the correct cathode, anode, and electrolyte for a given plating scenario.

How electroplating works

Electroplating uses electrolysis to coat one metal with a thin layer of another metal. The setup is:

Component	What it is	Why
Cathode (negative electrode)	The object to be plated	Metal ions are attracted to the negative electrode and deposited here
Anode (positive electrode)	A piece of the plating metal	Dissolves during electrolysis to replace the metal ions in the solution
Electrolyte	A solution containing ions of the plating metal	Provides the metal ions that will form the coating

Example: Silver plating a steel spoon

• Cathode: the steel spoon (object to be plated)
• Anode: a piece of pure silver
• Electrolyte: silver nitrate solution (AgNO₃)

Electrode reactions

At the cathode (the spoon): Ag⁺(aq) + e⁻ → Ag(s) — silver ions are reduced and deposited on the spoon

At the anode (the silver block): Ag(s) → Ag⁺(aq) + e⁻ — silver atoms are oxidised and dissolve into the solution

The silver anode gradually gets smaller as it dissolves. The concentration of Ag⁺ ions in the solution remains approximately constant because the anode replaces the ions that are deposited at the cathode.

Key principles to remember

1. The object to be plated is always the cathode (negative electrode)
2. The plating metal is usually the anode (positive electrode)
3. The electrolyte must contain ions of the plating metal
4. The plating metal is deposited at the cathode by reduction
5. The anode dissolves by oxidation, replenishing the metal ions

Common electroplating applications

Plating metal	Object plated	Purpose
Silver	Cutlery, trophies	Attractive appearance at lower cost than solid silver
Gold	Jewellery, connectors	Appearance; excellent electrical contact; corrosion resistance
Chromium	Car bumpers, taps, bicycle parts	Hard, shiny, corrosion-resistant surface
Tin	Steel food cans	Prevents corrosion; tin is non-toxic
Nickel	Various metal objects	Base layer before chromium plating; corrosion resistance
Zinc	Steel objects (galvanising)	Corrosion protection (electrogalvanising)
Copper	Printed circuit boards	Good electrical conductivity

Reasons for electroplating

1. Appearance

A thin layer of an attractive metal (silver, gold, chromium) makes the object look like it is made entirely of the expensive metal, at a fraction of the cost.

2. Corrosion prevention

A coating of a corrosion-resistant metal (chromium, tin, nickel) protects the base metal from water and oxygen. Unlike galvanising, most electroplated coatings only provide barrier protection — if scratched, the base metal underneath may corrode.

3. Hardness and durability

Chromium plating provides a hard, scratch-resistant surface. This extends the life of the object.

4. Electrical conductivity

Gold plating on electrical connectors ensures low-resistance contacts that do not corrode.

Factors affecting the quality of the coating

Factor	Effect
Current	Too high = rough, uneven coating; too low = very slow deposition
Time	Longer plating time = thicker coating
Concentration of electrolyte	Higher concentration = more ions available for deposition
Temperature	Higher temperature = faster deposition (ions move faster)
Cleanliness of cathode	Grease or oxide on the surface prevents even coating

Electroplating vs other coating methods

Method	How applied	Type of protection	Even coating?
Electroplating	Electrolysis	Barrier	Yes (very even)
Hot-dip galvanising	Dipping in molten zinc	Barrier + sacrificial	Thicker but less even
Painting	Brush/spray	Barrier only	Variable
Plastic coating	Dipping/spraying	Barrier only	Moderate

Worked exam question

Describe how you would electroplate a steel key with copper. State: (a) the cathode [1], (b) the anode [1], (c) a suitable electrolyte [1], (d) the cathode reaction [1].

(a) The steel key [1]

(b) A piece of pure copper [1]

(c) Copper(II) sulfate solution / CuSO₄(aq) [1]

(d) Cu²⁺(aq) + 2e⁻ → Cu(s) [1]

Common exam mistakes

1. Making the object to be plated the anode — it must be the cathode (negative electrode), where reduction deposits the metal.
2. Using the wrong electrolyte — if you are plating with silver, the electrolyte must contain Ag⁺ ions (e.g. silver nitrate solution), not just any conducting solution.
3. Saying the coating gets thicker at the anode — deposition occurs at the cathode. The anode dissolves.
4. Confusing electroplating with sacrificial protection — electroplating provides a barrier coating; sacrificial protection works electrochemically because the coating metal is more reactive.