Question

Which one of the following statements about the zeolites is false ?

• A. They are used as cation exchangers
• B. They have open structure which enables them to take up small molecules
• C. Zeolites are aluminosilicates having three dimensional network
• D. Some of the $SiO_4^{ 4 - }$ units are replaced by $ AlO_4^{ 5 - }$ and $ AlO_6^{ 9 - } $ ions in zeolites

Answer 1

The Correct Option is D

To determine the false statement about zeolites, let us review the properties and structure of zeolites:

1. Zeolites as Cation Exchangers:

   Zeolites have an open structure that allows ions and molecules to be exchanged efficiently. They are often used as cation exchangers in water softening and purification processes. This statement is true.

2. Open Structure of Zeolites:

   Zeolites indeed have an open, porous structure that allows them to accommodate small molecules. This porous nature is a defining property, making them effective adsorbents and catalysts. Therefore, this statement is true.

3. Zeolites as Aluminosilicates:

   Zeolites are classified as aluminosilicates, composed of a three-dimensional framework of SiO₄ and AlO₄ tetrahedra linked together by shared oxygen atoms. This is an accurate description of their structure and thus, the statement is true.

4. Replacement of SiO₄^4- Units:

   This statement suggests that in zeolites, some SiO₄^4- units are replaced by AlO₄^5- and AlO₆^9- ions. In reality, while aluminum can replace silicon in the tetrahedral framework of zeolites, they maintain a four-coordinate geometry; hence, AlO₄^5- replacement is true, but AlO₆^9- (six-coordinate aluminum) is incorrect in the context of zeolite structure. Hence, this statement is false.

After reviewing each option, it is clear that the statement "Some of the $SiO_4^{4-}$ units are replaced by $AlO_4^{5-}$ and $AlO_6^{9-}$ ions in zeolites" is the incorrect one because only the AlO₄^5- replacement aligns with zeolite chemistry, not AlO₆^9-.