Electroplating a metal object
Choose the electrode connections and electrolyte needed to coat an object with another metal.
Core and Extended · Chemistry 0620, 2026–2028. Half-equations and detailed charge transfer are taught in the Extended lesson.
Before you begin
- Know that metal forms at the cathode during suitable electrolysis.
- Recognise that an electrolyte must contain mobile ions.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
At which electrode does a suitable metal ion form metal in electrolysis?
What you will learn
- Explain why objects are electroplated.
- Describe the cathode, anode and electrolyte in a simple metal-plating arrangement.
The object receiving the coating is the cathode
Electroplating coats an object with a layer of another metal to improve its appearance or resistance to corrosion. In a simple arrangement using a soluble plating-metal anode, connect the object to the negative terminal as the cathode, use the coating metal as the positive anode and choose an electrolyte containing ions of the coating metal. A copper-plated object therefore needs copper ions, rather than merely a solution containing ions of the object's original metal.
The object's surface is prepared so the coating can adhere evenly. Metal from the electrolyte deposits on the cathode, while the metal anode dissolves and replenishes coating-metal ions in the simple model. Students should explain the role of each component in a diagram rather than treat a shiny finish as proof that any electrolyte or electrode connection will work.
A coating has a purpose and limitations
A decorative layer can change colour and finish while reducing the amount of an expensive surface metal required. A protective layer can reduce contact between the object and its environment. Its effectiveness depends on the coating material, adhesion and whether the layer stays intact; a damaged coating does not automatically keep protecting exposed material.
For copper plating, the metal object gains a copper coating at the cathode and the copper anode loses material. Reversing the connections will not simply coat the object in the same way. Detailed electron half-equations are Extended, but the Core explanation still needs the electrode signs, coating-metal ions and reasons for plating to be clear.
Pause and explain
Which electrolyte is appropriate for simple copper plating?
Worked example
Describe a simple arrangement for copper-plating a metal key, and state two possible reasons for electroplating.
Show the worked solution
- Connect the key as the negative cathode and a copper electrode as the positive anode.
- Use an electrolyte containing copper ions; copper deposits on the prepared key while the soluble copper anode supplies more copper ions.
- Reasons include changing appearance and improving resistance to corrosion when an appropriate intact coating is used.
Answer Key at the negative cathode; copper anode; copper-ion electrolyte.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Label the object, metal anode and electrolyte for nickel-plating a metal object using a soluble nickel anode.
Give me a hint
The receiving object is negative and the coating metal must be available as ions.
Compare my reasoning
- Connect the object to the negative terminal as cathode.
- Connect nickel to the positive terminal as anode.
- Choose an electrolyte containing nickel ions, which can deposit nickel on the object.
Object: negative cathode; nickel: positive anode; electrolyte: nickel-ion solution.
Look for these in your work
- The receiving and supplying electrodes are distinguished.
- The electrolyte matches the coating metal.
Explain why a small amount of a decorative surface metal can be used to improve an object's appearance by electroplating.
Give me a hint
Only the surface needs the chosen finish rather than the whole object's bulk.
Compare my reasoning
- The object's main material provides its bulk shape and structure.
- A layer of the decorative metal is deposited on the cathode surface.
- This gives the surface finish while using less of the decorative metal than making the whole object from it.
A thin deposited surface layer changes the finish without requiring the entire object to be made from that metal.
Look for these in your work
- Surface and bulk roles are separated.
- The appearance benefit is linked to the plating method.
A proposed copper-plating cell has the key at the positive electrode and an electrolyte containing only sodium chloride. Identify and correct the two design errors.
Give me a hint
Check both the receiving electrode sign and the source of coating-metal ions.
Compare my reasoning
- The key should be the negative cathode, where copper is deposited.
- The electrolyte must contain copper ions; sodium chloride alone does not supply them.
- For the simple model, use a positive soluble copper anode with the correctly prepared key.
Make the key the negative cathode and supply copper ions, with a copper anode in the stated simple arrangement.
Look for these in your work
- Both faults are explained rather than only relabelled.
- Each correction supports copper deposition.
Common mistakes
- Making the object to be coated the positive anode.
- Using an electrolyte without ions of the coating metal.
- Assuming any scratched decorative coating always prevents corrosion.
What can you explain now?
In a simple silver-plating cell with a silver anode, which electrode connection should the object receiving silver have?
Compare with the explanation
Negative cathode
The coating metal deposits at the cathode; silver ions in the electrolyte supply the silver coating.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Draw a plating cell for a chosen metal. Name what receives the coating, what supplies it, and why the electrolyte must contain that metal's ions.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.