Electroplating is a process where a thin layer of metal is deposited onto a conductive object using electrolysis. The key components and their roles are:

• Electrolyte Solution: This is an aqueous solution containing ions of the metal to be deposited. For example, a solution of copper sulfate (CuSO₄) would be used to electroplate with copper ions.
• Anode: This is the object to be coated with the metal. It is connected to the positive terminal of a DC power supply. The anode dissolves, releasing metal ions into the electrolyte.
• Cathode: This is a conductive object (usually made of the metal being deposited) immersed in the electrolyte solution. It is connected to the negative terminal of the DC power supply. Metal ions from the electrolyte are attracted to the cathode and gain electrons, depositing as a thin layer of metal.
• DC Power Supply: Provides the electrical potential difference to drive the electrolytic reaction.

During electroplating, the anode dissolves, releasing metal ions into the electrolyte. These ions migrate towards the cathode, where they gain electrons and deposit as a metallic coating on the cathode's surface. The process continues until a sufficient thickness of metal has been deposited.

Anode: The anode is the positive electrode where oxidation occurs. In the electrolysis of aqueous copper(II) sulfate using copper electrodes, copper ions (Cu²⁺) are oxidized to form elemental copper. The half-reaction is:

Cathode: The cathode is the negative electrode where reduction occurs. Water is the most likely species to be reduced in aqueous solution. The half-reaction is:

Therefore, at the anode, copper metal is deposited, and at the cathode, hydrogen gas is evolved. The copper electrode acts as the cathode, facilitating the deposition of copper metal.

Electroplating a brass key with chromium is beneficial because chromium is more resistant to corrosion than brass. Brass is an alloy of copper and zinc, and zinc is less noble (more reactive) than copper. Therefore, brass is susceptible to corrosion, particularly in humid environments.

Chromium is a more noble metal than both copper and zinc, meaning it is less reactive and more resistant to corrosion. When the key is electroplated with chromium, a thin layer of chromium is deposited onto the brass surface. This chromium layer acts as a protective barrier, preventing the corrosive substances in the environment (e.g., water, salts, oxygen) from reaching the underlying brass. The chromium layer effectively isolates the brass from the corrosive environment, significantly reducing the rate of corrosion.

The electrolyte solution contains chromium ions (Cr³⁺). These ions are attracted to the cathode (the key) and gain electrons, depositing as a chromium coating. The anode (often a chromium electrode) dissolves, releasing more chromium ions into the solution, maintaining the chromium concentration and ensuring the plating process continues. The relative reactivity series is important because it dictates which metal will be deposited. Chromium's position higher in the series than copper and zinc ensures that chromium ions are more likely to be reduced to metallic chromium than copper or zinc ions.