Question

Both Be and Al become passive on reaction with conc. \(\mathrm{HNO}_{3}\) because (1) they are non-reactive metals (2) of the non-reactive nature of the acid (3) of the formation of inert layer of oxide on the surface of metals (4) none of these

Short answer

3. They form an inert layer of oxide on their surface.

Step-by-step solution

- Understanding Passivation

Passivation is the process by which a material becomes 'passive,' that is, less affected by environmental factors such as air or water. In metals, this typically involves the formation of a protective oxide layer on the surface.

- Reaction of Be and Al with Concentrated \(\text{HNO}_{3}\)

When beryllium (Be) and aluminum (Al) react with concentrated nitric acid (HNO_{3}), they initially begin to oxidize. However, instead of continuing to react actively, they form a thin, protective layer of oxide on their surfaces that prevents further reaction.

- Formation of Inert Oxide Layer

This protective layer of oxide is inert, meaning it is stable and does not react further with nitric acid. This layer effectively 'passivates' the metal, making it less reactive under the conditions.

- Conclusion

Therefore, the correct answer is that Be and Al become passive on reaction with concentrated \(\text{HNO}_{3}\) because of the formation of an inert layer of oxide on the surface of the metals.

Key concepts

passivation process

Passivation is an essential concept in chemistry that refers to the process where a material, usually a metal, becomes less reactive when exposed to certain environmental conditions. This happens because a thin, protective layer forms on the material's surface. In metal passivation, this protective layer is often an oxide layer. This layer stops further reactions from occurring on the metal surface, making the metal 'passive' or less reactive.

Passivation is crucial in various applications, such as preventing rust in metals, improving the durability of materials, and ensuring the longevity of metal components in harsh environments. One real-world example is the use of stainless steel in construction and kitchen utensils, where the metal is passivated to prevent corrosion.

protective oxide layer

A protective oxide layer is a layer of oxide that forms on the surface of a metal during the passivation process. This layer acts as a barrier, preventing further chemical reactions between the metal and its environment.

In the case of beryllium (Be) and aluminum (Al), when they react with concentrated nitric acid (HNO₃), they form oxide layers. For beryllium, this oxide layer is beryllium oxide (BeO), while for aluminum, it is aluminum oxide (Al₂O₃). These oxide layers are inert, meaning they are stable and unreactive under typical conditions.

The formation of this protective layer is significant because it protects the underlying metal from further attacks by the acid or other corrosive agents. This increases the metal's durability and prolongs its life span.

reaction with nitric acid

The reaction of beryllium (Be) and aluminum (Al) with concentrated nitric acid (HNO₃) serves as a classic example of passivation. When these metals come into contact with concentrated nitric acid, they initially oxidize, starting a chemical reaction.

However, instead of continuing to react vigorously, they quickly form a protective oxide layer on their surfaces. For beryllium, this forms BeO, and for aluminum, it forms Al₂O₃. This thin layer prevents further interaction between the metal and the acid, effectively making the metal 'passive.'

This process highlights the importance of the protective oxide layer in safeguarding metals from further chemical reactions. The ability of nitric acid to passivate metals like Be and Al demonstrates why these metals are resistant to corrosion in environments where nitric acid is present.