Problem 18 - A Complete Resource Book in Chemistry for JEE Main

Question

The chemical formula of zeolite is ..... (a) \(\mathrm{Na}_{2} \mathrm{Al}_{2} \mathrm{Si}_{2} \mathrm{O}_{\mathrm{g}} \cdot \mathrm{xH}_{2} \mathrm{O}\) (b) \(\mathrm{Na}_{2}\left(\mathrm{Na}_{4}\left(\mathrm{PO}_{3}\right)_{6}\right.\) (c) \(\mathrm{Ca}_{2} \mathrm{Al}_{2} \mathrm{Si}_{2} \mathrm{O}_{8}\) (d) \(\mathrm{K}_{2} \mathrm{Al}_{2} \mathrm{Si}_{2} \mathrm{O}_{8} \times \mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

The chemical formula of zeolite is (a) \(\mathrm{Na}_{2} \mathrm{Al}_{2} \mathrm{Si}_{2} \mathrm{O}_{x} \cdot \mathrm{xH}_{2} \mathrm{O}\).

Step 1: Identify What Zeolite Is

Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents and catalysts. Their basic structure includes aluminum, silicon, and oxygen, often combined with sodium (Na) or other cations and water.

Step 2: Analyze the Options

Examine each provided option to determine which matches the basic composition criteria associated with zeolites, which typically consist of aluminosilicate materials with sodium and water molecules.

Step 3: Evaluate Option (a)

Option (a) has the formula \(\mathrm{Na}_{2} \mathrm{Al}_{2} \mathrm{Si}_{2} \mathrm{O}_{x} \cdot \mathrm{xH}_{2} \mathrm{O}\). This aligns with a typical zeolite structure, containing sodium, aluminum, silicon, oxygen, and water.

Step 4: Evaluate Other Options

- Option (b): \(\mathrm{Na}_{2}\left(\mathrm{Na}_{4}\left(\mathrm{PO}_{3}\right)_{6}\right)\) contains phosphate groups, which are not typical of zeolites.- Option (c): \(\mathrm{Ca}_{2} \mathrm{Al}_{2} \mathrm{Si}_{2} \mathrm{O}_{8}\) has calcium instead of sodium and lacks the water component.- Option (d): \(\mathrm{K}_{2} \mathrm{Al}_{2} \mathrm{Si}_{2} \mathrm{O}_{8} \times \mathrm{H}_{2} \mathrm{O}\) contains potassium instead of sodium.

Step 5: Conclusion on Correct Formula

Based on the given options and zeolite's typical composition, option (a)\(\mathrm{Na}_{2} \mathrm{Al}_{2} \mathrm{Si}_{2} \mathrm{O}_{x} \cdot \mathrm{xH}_{2} \mathrm{O}\) best fits the description of a zeolite.

Key Concepts

Chemical Formula of Zeolites

Zeolites have a unique chemical formula that distinguishes them from other minerals. This formula typically includes a set of elements: aluminum (Al), silicon (Si), oxygen (O), and often sodium (Na) or other cations.
These components combine to form the basic structure known as an aluminosilicate.
The chemical formula of zeolites can be generalized as \ \(\mathrm{Na}_{2}\, \mathrm{Al}_{2}\, \mathrm{Si}_{2}\, \mathrm{O}_{x} \cdot \mathrm{xH}_{2}\, \mathrm{O}\ \), where the presence of water molecules (denoted by \(\cdot\, \mathrm{xH}_{2}\mathrm{O}\)) is also significant.

• Aluminum and silicon form a tetrahedral framework.
• Cations like sodium are included to balance the negative charge from the aluminosilicate framework.
• Water molecules reside within the porous structure.

These features make zeolites versatile materials with significant uses in various industries.

Aluminosilicate Minerals

Zeolites belong to a larger group of compounds known as aluminosilicate minerals.
These minerals are characterized by their framework made from linked tetrahedra of aluminum and silicon, connected by shared oxygen atoms.
This intricate network results in a stable yet porous structure.

• The aluminum and silicon tetrahedra are critical to the strength and stability of zeolites.
• The framework's negative charge is compensated by positive cations such as Na\(^+\), K\(^+\), or Ca\(^{2+}\), depending on the specific zeolite.
• This unique structural feature allows for the absorption and exchange of ions.

Aluminosilicate minerals like zeolites are widely found in natural deposits, and they can also be synthesized industrially for specific applications.

Zeolites as Adsorbents and Catalysts

Zeolites are popularly used as adsorbents and catalysts, which are crucial in various chemical processes.
As adsorbents, zeolites are capable of attracting and holding molecules or ions onto their surface.
This is due to their porous structure with a high surface area.

• Their size and shape selective nature allow them to segregate molecules based on size.
• They can effectively remove water from gases and liquids, acting as desiccants.
• Their ion-exchange abilities make them useful in water softening.

In catalysis, zeolites provide a matrix for facilitating chemical reactions without being consumed in the process.

• Their ability to host and stabilize transition states is essential for driving chemical reactions.
• This property makes them invaluable in processes like hydrocracking and fluid catalytic cracking in oil refineries.
• Their uniform pore size allows specific chemical reactions to occur selectively.

Overall, zeolites' role as adsorbents and catalysts highlights their importance in industrial applications from environmental cleanup to fuel production.