Question

The formula for permutit or zeolite which is used as softer in the ion-exchange method is:
A. $NaAlSi{O}_{4}$
B. $NaAl{O}_{2}$
C. both A and B
D. ${Na}_{2}S{O}_{4}$

Answer 1

Hint: Zeolite are the crystals that are made up of silicon, aluminium and oxygen. They are noted for their liability towards the reversible dehydration and ion-exchange.

Complete step by step answer:
- Any member of the family of the hydrated aluminosilicate minerals which contain alkali and alkaline-earth metals are known as zeolites.
- And permutit is known as the artificial zeolite or as the man-made zeolite.
- The chemical formula of zeolite can be written as ${Na}_{2}.{Al}_{2}{O}_{3}.nSi{O}_{2}.x{H}_{2}O$.
- Zeolite is known to be made up of non-porous minerals. These minerals have the capability of exchanging ions. Hence, zeolite is used in removing the hardness of the water.
- This is because zeolite contains sodium and aluminium which makes the water soft in nature. The hardness of the water is due to the presence of calcium and magnesium ions.
- Hard water is allowed to pass through the reservoir which has a permutit packed into it.
- When the water passes through the permutit, the compound undergo an exchange of ions.
- This means that the calcium and magnesium ions present in the hard water get replaced by sodium and aluminium present in the permutit.
- The following reaction takes place.

$\underset { Permutit }{ { Na }_{ 2 }{ Al }_{ 2 }{ Si }_{ 2 }{ O }_{ 8 }.x{ H }_{ 2 }O } \quad +\quad { Ca }^{ 2+ }(or\quad { Mg }^{ 2+ })\quad \longrightarrow \underset { Exhausted\quad Permutit }{ Ca{ Al }_{ 2 }{ Si }_{ 2 }{ O }_{ 8 }.x{ H }_{ 2 }O } \quad +\quad { Na }^{ + }$

Thus, the formula of permutit or zeolite which is used as softer in the ion-exchange method is ${Na}_{2}{Al}_{2}Si{O}_{2}{O}_{8}.x{H}_{2}O$. Hence, the correct answer is none of the above.

Note: Zeolites have a framework with cavities and channels inside it, where the cations, water or small molecules may reside. This property of zeolite is used to separate molecules that are of certain sizes and shapes that can pass through. It is also used as traps for molecules for analysis.