Question

1) Explain why aluminium phosphate, AlPO4 form in quartzlike structures like SiO2. (Hint: How are aluminium and phosphorus related electronically to silicon? How would an AlP pair be related to two silicon atoms?)

2) On the basis of the structures, explain why zeolites are called sieves

Answer 1

1.

The reason that aluminium phosphate is able to have the same structure as quartz is because the aluminum and phosphorus ions are of similar size to silicon ions. Thus the same structure can be achieved since the aluminums and phosphorus can completely replace the silicons without alteration of the quartz structure.

2.

Molecular sieve has unique structure which allows the water of crystallization to be removed, leaving a porous crystalline structure. These pores or "cages" have a high affinity to re-adsorb water or other polar molecules. Hence the case.