Write a short note on zeolites.

Explanation

Zeolites are three dimensional alumino silicates. If some silicon atoms in three dimensional network silicon dioxide are replaced by aluminium atoms, the alumino silicate formed will have some negative charge. To balance these negative charges some extra cations such as `Na^+,K^+ " or " Ca^(2+)` will present in these silicates. Examples are `ZSM - 5` which is used as a catalyst in direct conversion of alcohols into gasoline. Hydrated zeolites are used as ion exchangers in softening of hard water.
The structure of zeolite permits the formation of cavities of different sizes. Molecules like `H_2O,NH_3,CO_2` can be trapped in these cavities. Thus they can serve as molecular sieves.