Question
What is electroplating? Explain the process with a simple experiment showing how copper can be deposited on an iron spoon.
Solution — Step by Step
Electroplating is the process of depositing a thin layer of a metal onto the surface of another object (called the substrate) using electricity. The deposited layer is called the electroplate.
It works by passing electric current through an electrolytic solution containing ions of the plating metal. The object to be plated is made the cathode (negative electrode). The plating metal is made the anode (positive electrode).
Materials needed:
- Iron spoon (to be plated)
- Copper strip (source of copper)
- Copper sulphate solution (electrolyte, provides Cu²⁺ ions)
- Battery (6V)
- Connecting wires
- Beaker
Setup:
- Fill the beaker with copper sulphate solution (CuSO₄, blue coloured)
- Connect the iron spoon to the negative terminal of the battery → the spoon becomes the cathode
- Connect the copper strip to the positive terminal → copper becomes the anode
- Dip both electrodes into the copper sulphate solution
- Switch on the current
At the cathode (iron spoon — negative electrode):
Cu²⁺ ions from the solution are attracted to the negatively charged spoon. They gain electrons (are reduced) and deposit as copper metal:
The spoon gradually acquires a shiny copper coating.
At the anode (copper strip — positive electrode):
Copper metal at the anode loses electrons (is oxidised) and dissolves into the solution as Cu²⁺ ions:
The copper anode gradually dissolves, maintaining the Cu²⁺ concentration in solution.
Net result: Copper is transferred from the anode to the cathode — the spoon is copper-plated, and the copper strip gradually wears away.
Electroplating is done for several reasons:
- Corrosion protection: Zinc-plated iron (galvanised iron) is used in construction and vehicles — zinc protects iron from rusting
- Decorative purposes: Silver-plated cutlery, gold-plated jewellery, chromium-plated taps and door handles
- Wear resistance: Chromium plating on machine parts
- Electrical conductivity: Gold plating on electrical connectors (gold resists corrosion and is an excellent conductor)
- Cost reduction: Thin layer of expensive metal (gold, silver) on cheap base metal gives the appearance and properties at a fraction of the cost
Why This Works
The process is a direct application of electrolysis. The key chemistry: metal ions in solution have a charge; they move toward oppositely charged electrodes under the influence of electric current. At the cathode (negative), positive metal ions are reduced to form the deposited layer. At the anode (positive), the metal is continuously replenished by oxidation.
The beauty of using a metal anode (rather than an inert electrode) is that the ion concentration in solution stays constant throughout the process — the anode dissolves at the same rate that metal deposits at the cathode.
Alternative Method
For exam purposes: “Electroplating is an application of Faraday’s laws of electrolysis.” The mass of metal deposited is proportional to the charge passed and inversely proportional to the number of electrons needed per ion (). This connects to the calculation formula .
Common Mistake
Students often describe the cathode and anode incorrectly. In electroplating:
- Cathode = object to be plated (connected to negative terminal → attracts positive metal ions)
- Anode = source metal (connected to positive terminal → dissolves to replenish ions)
A common confusion: students write “anode is the object to be plated.” This is exactly backwards. The anode LOSES metal; the cathode GAINS it.
CBSE Class 8 only requires the basic concept: object to be plated = cathode, source metal = anode, electrolyte contains ions of plating metal. For Class 10, also know: corrosion prevention (galvanising) and the difference between electroplating and electroforming. For Class 12 and JEE, the quantitative calculation using Faraday’s laws applies.