Electrolysis - Electroplating

Introduction

Electroplating is a process where a thin layer of one metal is deposited onto the surface of another metal object using electrolysis. This is done to improve the appearance, protect the object from corrosion, or enhance certain properties like wear resistance.

The Electroplating Process

The electroplating process involves using an electrolytic cell consisting of a positive electrode (anode) and a negative electrode (cathode). The object to be plated is connected to the cathode, and a metal (the plating metal) is used as the anode. The entire setup is immersed in a electrolyte solution, which contains ions of the metal to be deposited.

Components of an Electroplating Cell

• Anode: The metal that is being plated off.
• Cathode: The object to be plated.
• Electrolyte: A conductive solution containing ions of the metal to be deposited.
• Power Supply: Provides the electrical energy to drive the electrolysis.

Steps in Electroplating

1. Preparation: The object to be plated is cleaned to remove any dirt, grease, or oxides.
2. Electrolyte Solution: The anode is made from the plating metal, and the electrolyte solution contains ions of this metal.
3. Immersion: Both the anode and the object to be plated are immersed in the electrolyte solution.
4. Applying Current: A direct current (DC) is passed through the electrolytic cell.
5. Ion Migration: The positive metal ions in the electrolyte are attracted to the negative cathode (the object to be plated). The negative ions (if present) are attracted to the positive anode (the plating metal).
6. Deposition: At the cathode, the metal ions gain electrons and are reduced to metal atoms, which then deposit as a thin layer on the cathode's surface.
7. Anode Reaction: At the anode, the plating metal atoms lose electrons and are oxidized to metal ions, which enter the electrolyte solution.

Chemical Reactions

During electroplating, the following reactions occur:

• At the Cathode (Reduction): $M^{n+}(aq) + ne^- \rightarrow M(s)$ (where M is the plating metal and n is its charge)
• At the Anode (Oxidation): $M(s) \rightarrow M^{n+}(aq) + ne^-$

Factors Affecting Electroplating

Factor	Effect
Current Density	Higher current density leads to a faster deposition rate.
Electrolyte Concentration	Higher concentration of metal ions increases the deposition rate.
Temperature	Higher temperature generally increases the deposition rate (within reasonable limits).
Nature of Electrolyte	The electrolyte must be able to conduct electricity and contain the ions of the metal to be deposited.

Examples of Electroplating

• Silver plating is used to enhance the appearance and protect cutlery and decorative items.
• Chrome plating is used to provide a hard, durable, and corrosion-resistant coating on car bumpers and other metal parts.
• Gold plating is used to add a decorative finish and prevent tarnishing to jewelry.