Question

When hydrated sodium aluminium silicate, which is zeolite, is treated with hard water, the sodium ions are exchanged with:
A.$C{a^{2 + }}$
B.$O{H^ - }$ ions
C.$M{g^{2 + }}$ ions
D.$Si{O_4}^{2 - }$

Answer 1

Hard water: It is defined as the water which contains calcium and magnesium salts. Zeolites: These are defined as the crystalline solid of silicon, aluminium and oxygen. They are generally used as catalysts and adsorbents.

Complete step by step solution:
Let us first read about hard water and its disadvantages and then we will talk about zeolites.
Hard water: It is defined as the water which contains calcium and magnesium salts of carbonates, bicarbonates and sulphates. When any person tries to use hard water for washing clothes then he will face difficulty because soaps or detergents are not soluble in hard water. And hence the clothes will remain dirty. Drinking hard water is safe to our health as it contains minerals. And also it is good for our teeth.
Soft water: The normal filtered water is known as soft water. It generally contains sodium and its salts.
Zeolites: These are defined as the crystalline solid of silicon, aluminium and oxygen. They are generally used as catalysts and adsorbents. They are also known as molecular sieves.
Catalysts: They are defined as the molecules which do not take part in the reaction but can enhance the rate of reaction i.e. either increase the reaction or decrease the reaction.
Adsorbents: During adsorption the molecule or the surface on which adsorption is happening, is known as adsorbents.
Now in the question we are given with hydrated sodium aluminium silicate, which is zeolite. Now it is asked that when sodium aluminium silicate is heated with hard water then sodium ions are exchanged by which ion.
The reaction between sodium aluminium silicate with hard water is as follows:
Let's suppose hard water contains chlorides. Then the reaction will be as:
${\text{MgC}}{{\text{l}}_{\text{2}}}{\text{ + 2N}}{{\text{a}}^{\text{ + }}} \to {\text{Mg(Al - silicate}}{{\text{)}}_{\text{2}}}{\text{ + 2NaCl}}$
$CaC{l_2} + 2N{a^ + } \to Ca{(Al - silicate)_2} + 2NaCl$.
Hence during the reaction of zeolite i.e. sodium aluminium silicate with hard water the sodium ion of zeolite will be exchanged with calcium and magnesium ions.

So option B and D i.e. $C{a^{2 + }}$ and $M{g^{2 + }}$ are correct.

Note: Adsorption is defined as the process of deposition of molecular species onto the surface of another species. The molecular species on which molecules are adsorbed are known as adsorbent and the species which are being adsorbed are known as adsorbate.