Question

Softening of hard water is done using sodium aluminium silicate (zeolite). This causes:

• A. adsorption of $C{a}^{2+}$and $M{g}^{2+}$ ions of hard water replacing $A{l}^{3+}$ ions.
• B. none of these
• C. both (a) and (b)
• D. adsorption of $C{a}^{2+}$ and $M{g}^{2+}$ ions of hard water replacing $N{a}^{+}$ ions

Answer 1

The correct option is D adsorption of $C{a}^{2+}$ and $M{g}^{2+}$ ions of hard water replacing $N{a}^{+}$ ions

$\text{Action of zeolites}$

The hardness of water is due to bicarbonates, chlorides and sulphates of $C{a}^{2+}$ and $M{g}^{2+}$ ions. When sodium aluminium silicate (zeolite) is added, $N{a}^{+}$ replaces $C{a}^{2+}$ and $M{g}^{2+}$ by adsorption, and hence water becomes soft.

$\text{Reactions depicting the chemical change}$

$N{a}_{2}Ze+Ca(HC{O}_3{)}_2\to CaZe+2NaHC{O}_3$

$N{a}_{2}Ze+Mg(HC{O}_3{)}_2\to MgZe+2NaHC{O}_3$

$N{a}_{2}Ze+CaC{l}_2\to CaZe+2NaCl$

$N{a}_{2}Ze+MgS{O}_4\to MgZe+N{a}_{2}S{O}_4$
(Zeolite) (Hardness)

So, option (a) is the correct answer.