Chemistry – Electrochemistry - Electrolysis | e-Consult

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.