Electroplating Concepts Chemistry Tutorial

Key Concepts

• Electroplating is also known as electrodeposition.
• Electroplating uses an electrolytic cell to deposit a coating of one metal onto another metal.
  
• Setting up a typical electrolytic cell for electroplating:

1. The object to be plated (coated with a different metal) is made the cathode (negative electrode) by connecting it to the negative terminal of the power supply.
2. The metal to be plated onto the object is made the anode (positive electrode) by connecting it to the positive terminal of the power supply¹.
3. The electrolyte contains the metallic ions of the metal to be plated onto the object.
   The electolyte may be either a liquid (molten salt) or an aqueous solution, but is usually an aqueous solution.

• Electrochemical Processes:

1. At the anode (positive electrode), metal ions are oxidized and enter the electrolyte as mobile ions:

   M_(s) → M⁺ + e^-

   
   The anode will disintegrate in time as the metal atoms, M_(s), are converted to metal ions, M⁺.
2. At the cathode (negative electrode), metal ions from the electrolyte are reduced:

   M⁺ + e^- → M_(s)

   
   Solid metal, M_(s), is deposited on the cathode.
3. The concentration of metal ions, [M⁺], in the electrolyte should remain constant during this process since just as many cations are being produced at the anode as are being used up at the cathode².

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Example: Silver Plating

Electroplating is used to produce silver-plated cutlery and jewellery.

• Electrolyte: a solution containing silver ions, Ag⁺.

  Commercially, silver cyanide, AgCN, is traditionally used because it produces a good coverage of solid silvery silver, but, cyanide ions, CN^-, are extremely toxic.
  In the school laboratory, an aqueous silver nitrate solution, AgNO_3(aq), can be used, but, this usually results in a black coating of crystalline silver.

• Anode (positive electrode): a silver rod, Ag_(s).

  Oxidation (loss of electrons) occurs at the anode:

  Ag_(s) → Ag⁺_(aq) + e^-

  
  Silver rod disintegrates over time.

• Cathode (negative electrode): the object to be plated (for example a steel spoon)

  Reduction (gain of electrons) occurs at the cathode:

  Ag⁺_(aq) + e^- → Ag_(s)

  
  The object becomes plated in solid silver, Ag_(s), over time.