What is the principle of electroplating? How is electroplating of chromium carried out?

Principle of Electroplating:

The principle of electroplating is based on the reduction of metal ions at the cathode (the object to be plated) in an electrolytic cell. When a direct current is passed through an electrolyte solution containing metal ions, the metal ions are reduced onto the surface of the object, forming a thin, adherent metal layer.

The basic electroplating reaction is:

Metal2+(aq)+2e−→Metal(s)

This reaction involves the transfer of electrons from the cathode (where reduction occurs) to the metal ions in the electrolyte, leading to the deposition of metal on the surface of the cathode.

Electroplating of Chromium:

Chromium electroplating is done using a chromic acid solution, which contains chromium trioxide (CrO₃) and sulfuric acid. The electroplating of chromium is primarily used to provide a hard, corrosion-resistant surface for objects such as automotive parts, tools, and machinery.

Process of Chromium Electroplating:

  1. Preparation of Electrolyte Solution:

    • The electrolyte used for chromium plating contains chromic acid (CrO₃) and sulfuric acid (H₂SO₄) as additives. The concentration of chromic acid is usually between 200-300 g/L, and sulfuric acid is added to increase the efficiency of the plating process.

  2. Setup of Electroplating Cell:

    • The object to be plated (cathode) is connected to the negative terminal of the power supply.

    • A chromium anode (positive terminal) is used. In some cases, the anode may be made of pure chromium or a lead alloy covered with chromium.

  3. Electroplating Process:

    • When a direct current is applied, chromium ions (Cr³⁺) in the electrolyte solution are reduced onto the surface of the object being plated, forming a chromium coating:

      Cr3+(aq)+3e−→Cr(s)

    • The chromium ions come from the chromic acid in the electrolyte, and the anode slowly dissolves to replenish the chromium ions in the solution.

  4. Post-Plating Treatment:

    • After electroplating, the object is rinsed and may be subjected to polishing or other treatments to improve the appearance or surface hardness.

Applications of Chromium Electroplating:

  • Chromium plating is used to improve the hardness, wear resistance, and corrosion resistance of metal surfaces.

  • It is widely used in the automotive industry for plating bumpers, wheels, and other parts to enhance their aesthetic appeal and durability.

Related Questions:

  1. What is electroplating? Write down the procedure of electroplating.
  2. How does calcium metal react with dilute H₂SO₄?
  3. How is electroplating of tin on steel carried out?
  4. In electroplating of chromium, which salt is used as an electrolyte?
  5. Find out the oxidation numbers of the underlined elements in the following compounds:
  6. How can a non-spontaneous reaction be carried out in an electrolytic cell? Discuss in detail.
  7. Discuss the electrolysis of water.
  8. Discuss the construction and working of a cell in which electricity is produced.
  9. How can we prepare NaOH on a commercial scale? Discuss its chemistry along with a diagram.
  10. Discuss the redox reaction taking place in the rusting of iron in detail.
  11. Discuss why galvanizing is considered better than tin plating.
  12. Choose Arrhenius acids from the following compounds: HF, NH₃, H₂SO₄, SO₂, H₂S, H₂O
  13. Which salt is formed when HCl reacts with BaCO₃?
  14. How will you justify that H₂SO₄ is a Bronsted-Lowry acid?
  15. Define oxidation in terms of electrons. Give an example.
  16. Define reduction in terms of loss or gain of oxygen or hydrogen. Give an example.
  17. What is the difference between valency and oxidation state?
  18. Differentiate between oxidizing and reducing agents.
  19. Differentiate between strong and weak electrolytes.
  20. Why is steel plated with nickel before the electroplating of chromium?