Question

The chemical formula of zeolite is:
a) \[{{K}_{2}}A{{l}_{2}}S{{i}_{2}}{{O}_{8}}.x{{H}_{2}}O\]
b) \[C{{a}_{2}}A{{l}_{2}}S{{i}_{2}}{{O}_{8}}\]
c) \[N{{a}_{2}}A{{l}_{2}}S{{i}_{2}}{{O}_{8}}.x{{H}_{2}}O\]
d) \[N{{a}_{2}}(N{{a}_{4}}{{(P{{O}_{4}})}_{6}})\]

Answer 1

Hint: Zeolites are crystalline solids structures which are generally made of silicon, aluminum and oxygen that form a framework with cavities and channels inside where cations, water or small molecules may reside. They are often also referred to as molecular sieves. The general formula for zeolites can be written as:
\[{{M}_{{x}/{n}\;}}\left[ {{\left( Al{{O}_{2}} \right)}_{x}}{{(Si{{O}_{2}})}_{y}} \right].m{{H}_{2}}O\]
where cations M of valence n neutralize the negatively charged zeolite framework.

Complete step by step answer:
1. Zeolites are good shape selective structures which act as catalysts because of their honeycomb like structures.
2. They are microporous aluminosilicates with a network of silicates which are three dimensional, in which the silicon atoms are replaced by the aluminum atoms giving it Al-O-Si framework. The chemical formula for zeolites can be written as \[{{Na}_{2}}A{{l}_{2}}S{{i}_{2}}{{O}_{8}}.x{{H}_{2}}O\].
3. The reactions which take place inside the zeolites are dependent upon the shape and size of the reactant and product molecules as well as on the pores and the cavities of the zeolites.
4. They can be found in nature as well as synthesized for catalytic selectivity, 245 unique zeolite frameworks have been identified, and over 40 naturally occurring zeolite frameworks are known.
5. Zeolites are widely used as the catalysts in petrochemical industries for the cracking of hydrocarbons and isomerization, one of the important zeolites used in petrochemical industries in ZSM-5 which converts alcohols directly into gasoline by dehydrating them to give a mixture of hydrocarbons.

So, the correct answer is (c).

Note: Zeolites can accommodate cations like \[N{{a}^{+}},\,{{K}^{+}},\,M{{g}^{2+}},C{{l}^{2+}}\].These positive ions are rather loosely held and can readily be exchanged for others in a contact solution.
Some examples are:
Erionite \[N{{a}_{2}}{{K}_{2}}CaMg{{(Al{{O}_{2}})}_{2}}{{(Si{{O}_{2}})}_{2}}.6{{H}_{2}}O\], Gemelinite \[N{{a}_{2}}Ca{{(Al{{O}_{2}})}_{2}}{{(Si{{O}_{2}})}_{4}}.6{{H}_{2}}O\]