Question

Identify the correct statements. (1) Beryllium liberates \(\mathrm{H}_{2}\) from \(\mathrm{HCl}\) or \(\mathrm{H}_{2} \mathrm{SO}_{4}\). (2) Beryllium is rendered passive on treatment with conc. \(\mathrm{HNO}_{3}\). (3) \(\mathrm{BeCl}_{2}\) has a polymeric structure in the solid state but exists as a dimmer in the vapour state. (4) \(\mathrm{BeCl}_{2}\) has a dimeric structure in the solid state but a polymeric structure in the vapour state. (a) 1,2 (b) 2,3 (c) \(1,2,3\) (d) \(2,3,4\)

Short answer

(b) 2,3

Step-by-step solution

Analyze Statement 1

Beryllium does not react with acids like hydrochloric acid (HCl) or sulfuric acid (H₂SO₄) to liberate hydrogen gas. This behavior is due to the formation of a resistant oxide layer on its surface, which prevents such reactions. Hence, statement (1) is incorrect.

Analyze Statement 2

Beryllium becomes passive when treated with concentrated nitric acid \(\mathrm{HNO}_3\). This passivation occurs because a protective oxide layer forms on its surface, preventing further reactions. Therefore, statement (2) is correct.

Analyze Statement 3

In the solid state, \(\mathrm{BeCl}_2\) forms a polymeric structure due to the bridging chlorine atoms that connect the beryllium atoms. In the vapor state, \(\mathrm{BeCl}_2\) exists as a linear chain or dimer due to the breakdown of the polymeric form. Therefore, statement (3) is correct.

Analyze Statement 4

The statement (4) claims \(\mathrm{BeCl}_2\) is dimeric in solid and polymeric in the vapor state, which is incorrect. As previously analyzed, \(\mathrm{BeCl}_2\) is polymeric in solid and dimeric in vapor state. Hence, statement (4) is incorrect.

Identify the Correct Combination

Based on the analysis, statements (2) and (3) are correct. Therefore, the correct combination of statements is (b) 2,3.

Key concepts

Passivation of Metals

Passivation is a fascinating phenomenon that prevents metals from reacting with their environments. When a metal like beryllium interacts with a certain chemical, a protective layer forms on its surface. In the case of beryllium, concentrated nitric acid (\(\mathrm{HNO}_3\)) induces this form of protection. This process is called passivation.
\(\mathrm{HNO}_3\) supplies oxygen, causing an oxide layer to develop on beryllium. This layer acts as a shield, stopping further aggressive chemical reactions with the metal.
This shield is critical for preserving metals, especially in environments where they might corrode or react undesirably.

• The protective layer is often incredibly thin, yet highly effective.
• It also slows down oxidation processes.
• In chemistry, understanding passivation is essential to manipulating metal properties.

Polymeric Structure

The concept of a polymeric structure is quite engaging. In chemistry, polymers are large molecules made by linking smaller units.
In the solid state, beryllium chloride (\(\mathrm{BeCl}_2\)) features a polymeric structure. This means that \(\mathrm{BeCl}_2\) molecules multiply to form long chains through shared chlorine atoms.
This connection occurs because bridging chlorine atoms join multiple beryllium atoms together into chains. In essence, it creates a network or a web of molecules.
- **Significance:** - Polymer structures provide stability and robustness to substances. - Understanding polymer structures is vital in material science for applications like plastics. - It can influence the material's melting and boiling points.Polymeric structures in beryllium compounds are keenly studied as they influence many practical applications and give the compound distinctive attributes.

Oxide Layer Formation

The formation of an oxide layer is a natural result of metal exposure to oxygen in various environments. This process forms a layer composed of metal oxides, like the one observed in beryllium.
This oxide layer is responsible for the metal’s increased resistance to further chemical attacks, drastically reducing corrosion and other reactions.
Here's how it works:

• The metal surface reacts with oxygen, forming a tight layer of oxides.
• This layer tightly adheres to the metal, preventing further diffusion of oxygen.
• As a result, the metal underneath is essentially blocked from additional reactions.

**Key Points to Remember:** - This layer is incredibly thin but immensely effective. - It’s a self-healing layer; if damaged, the exposure causes it to reform automatically. - Understanding this process is essential in protecting metals from environmental corrosion and increasing metal longevity.