Question

How does a zinc coating on iron protect the iron from unwanted oxidation? [Section 20.8]

Short answer

A zinc coating on iron protects the iron from unwanted oxidation by acting as a sacrificial anode, undergoing oxidation preferentially due to its higher reactivity compared to iron. This process, called cathodic protection, leads to the formation of a stable, protective layer of zinc oxide on the surface of the iron, preventing the iron from rusting. The application of the protective zinc coating to iron is known as galvanization.

Step-by-step solution

Understand oxidation process

Oxidation occurs when a material loses electrons to another material, often involving oxygen. In the case of iron, when it comes into contact with oxygen and moisture, it undergoes oxidation, forming iron oxide (rust). This can lead to structural damage and degradation of the iron as the rust flakes off, exposing more iron to the oxidation process.

Role of zinc in the oxidation process

Zinc is a more reactive metal compared to iron. Thus, when zinc is used as a coating on iron, it becomes the primary target for oxidation. Zinc undergoes oxidation by losing electrons to the oxygen and forming zinc oxide, which acts as a stable and protective layer on the surface of the iron.

Cathodic protection of iron by zinc

When zinc is used as a coating on iron, it acts as a sacrificial anode, a process called cathodic protection. The zinc coating willingly undergoes oxidation, protecting the iron beneath it from being oxidized. This is because zinc, being more reactive, has a greater tendency to lose electrons and form positive ions, as compared to iron. Thus, oxygen and other oxidizing agents will preferentially react with the zinc coating instead of the underlying iron surface.

Explain galvanization

Galvanization is the process of applying a protective zinc coating to iron or steel to prevent rusting. This process can be done in various ways, most commonly by hot-dip galvanizing, which involves immersing the iron or steel into molten zinc to form a zinc coating on the surface. This layer serves to protect the iron from the unwanted oxidation, ensuring the structural integrity of the iron remains intact.

Summarize the key points

In summary, a zinc coating on iron protects the iron from unwanted oxidation because zinc is more reactive than iron and undergoes oxidation preferentially. This process, known as cathodic protection, preserves the integrity of the underlying iron by creating a stable, protective layer of zinc oxide at the surface. The application of this protective zinc coating to iron is called galvanization.