Best Desiccant


 
Photo credited: WidgetCo
Which one is the best desiccant among the following compounds Fe (BrO4)3, Zn5(IO6)2, and [(C2H5)4N] [ClO4]?

Answering this question requires one to understand the meaning of desiccant and the chemistry of the provided compounds. Desiccant is a hygroscopic material. It prompts and keeps the state of dryness in its vicinity. This implies that it absorbs water. 

The characteristics of desiccant hinge on the coordination number of the central atom in complex compounds. The coordination number is the number of molecules of water in the propinquity of the neighboring central metal ion or atom. Moreover, it can be defined as the number of donor atoms bonded to a central metal atom or ion.

The coordination sphere contains a central atom or ion and ligands attached to it. The brackets in complex formula encircle coordination sphere. Therefore, this shows that species outside the brackets are not part of the coordination sphere.

Based on the explanation above, [(C2H5)4N] [ClO4] is the best desiccant because it has a larger coordination number as compared to Fe (BrO4)3 and Zn5(IO6)2. [(C2H5)4N] [ClO4] has a coordination number of 5 while Fe (BrO4)3 has coordination of 3, and Zn5(IO6)2 has a coordination number of 2. 

The central atom with a larger coordination number would bond with more water molecules than the central atom with a smaller coordination number. Hence, this ascertains that [(C2H5)4N] [ClO4] would bond with more water molecules than Fe (BrO4)3 and Zn5(IO6)2. In other words, it would absorb more water molecules.

Water molecules would replace (C2H5) and [ClO4] in [(C2H5)4N] [ClO4] complex, (IO6)2 in Zn5(IO6)2 complex, and (BrO4) in Fe (BrO4)3 complex.




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