Question

When zeolite which hydrated sodium aluminium silicate is treated with hard water, the sodium ions are exchanged with:
A) \[{{\text{H}}^{\text{ + }}}\]
B) \[{\text{M}}{{\text{g}}^{{\text{2 + }}}}\]
C) \[{\text{C}}{{\text{a}}^{{\text{2 + }}}}\]
D) Both \[{\text{M}}{{\text{g}}^{{\text{2 + }}}}\] and \[{\text{C}}{{\text{a}}^{{\text{2 + }}}}\]

Answer 1

Hint: The chemical formula of hydrated sodium aluminium silicate is \[{\text{N}}{{\text{a}}_{\text{2}}}{\text{A}}{{\text{l}}_{\text{2}}}{\text{S}}{{\text{i}}_{{\text{14}}}}{{\text{O}}_{{\text{32}}}} \cdot {\text{3}}{{\text{H}}_{\text{2}}}{\text{O}}\].
 Permutit is an artificial zeolite, known as hydrated sodium aluminium silicate. The chemical formula of hydrated sodium aluminium silicate is \[{\text{N}}{{\text{a}}_{\text{2}}}{\text{A}}{{\text{l}}_{\text{2}}}{\text{S}}{{\text{i}}_{{\text{14}}}}{{\text{O}}_{{\text{32}}}} \cdot {\text{3}}{{\text{H}}_{\text{2}}}{\text{O}}\]. It is used for water softening. The hardness of water depends on dissolved mineral content like \[{\text{C}}{{\text{a}}^{{\text{2 + }}}}\] and \[{\text{M}}{{\text{g}}^{{\text{2 + }}}}\] ions.

Complete answer:
Water containing bicarbonates, sulphates and chlorides of calcium and magnesium are termed hard water.
The hardness of water is of two types:
Temporary hardness: It is due to the presence of bicarbonates of calcium and magnesium. It can be removed by boiling or by adding calculated quantities of lime.
Permanent hardness: It is due to the presence of sulphates and chlorides of calcium and magnesium. Cannot be removed merely by boiling or by adding lime. It may be removed by permutit process.
Permutit process: In this process, artificial zeolite permutit is used for softening the water. Permutit is insoluble in water. It is placed in a suitable column and hard water is allowed to pass through it. The process removes both temporary and permanent hardness of the water.
Let us consider the abbreviated notation of zeolite is\[{\text{N}}{{\text{a}}_{\text{2}}}{\text{Z}}\].
\[{\text{N}}{{\text{a}}_{\text{2}}}{\text{Z + CaC}}{{\text{l}}_{\text{2}}} \to {\text{2NaCl + CaZ}}\]
\[{\text{N}}{{\text{a}}_{\text{2}}}{\text{Z + MgC}}{{\text{l}}_{\text{2}}} \to {\text{2NaCl + MgZ}}\]
Thus, we can say that when zeolite which hydrated sodium aluminium silicate is treated with hard water, the sodium ions are exchanged with both \[{\text{M}}{{\text{g}}^{{\text{2 + }}}}\] and\[{\text{C}}{{\text{a}}^{{\text{2 + }}}}\].

Hence, the correct option is (D) Both \[{\text{M}}{{\text{g}}^{{\text{2 + }}}}\] and\[{\text{C}}{{\text{a}}^{{\text{2 + }}}}\]

Note: Water containing minerals like \[{\text{C}}{{\text{a}}^{{\text{2 + }}}}\] and \[{\text{M}}{{\text{g}}^{{\text{2 + }}}}\]ions are known as hard water. The concentration of these minerals in water determines the hardness of the water. Hard water is not safe to use. So different techniques are used to remove the hardness of the water. One of the techniques is the permutit process that is based on the ion-exchange method.