Learning focus
Explain electrochemical and energetic processes using ions, electrons, balanced equations, observations, energy pathways and quantitative evidence.
Purpose
Metal objects are electroplated to improve appearance and resistance to corrosion. A thin coating can also increase surface hardness or reduce the amount of an expensive metal required.
Object as cathode
The object to be coated is connected to the negative terminal. Metal ions gain electrons on its surface and become metal atoms, creating the coating.
Anode and electrolyte
The plating metal is commonly used as the positive anode so it replenishes metal ions. The electrolyte contains ions of the coating metal, such as Cu2+ for copper plating or Ag+ for silver plating.
Surface preparation
The object must be cleaned to remove grease and oxide. Poor cleaning prevents adhesion and produces patchy deposits even when the electrical connections are correct.
Worked example
To silver-plate a spoon, connect the spoon as cathode, use silver as anode and use a solution containing Ag+ ions.
Practical or data skill
Draw and label a plating cell for copper-coating an iron object. Include polarity and ion movement.
Examination tip
The object being plated is the cathode, not the anode.
Review questions and suggested answers
Question 1
Why is the object made the cathode?
Suggested answer
Metal ions must gain electrons and deposit on it.
Question 2
What should the electrolyte contain?
Suggested answer
Ions of the metal used for the coating.
Question 3
Give one purpose of electroplating.
Suggested answer
Improved appearance or corrosion resistance.
