Question

How can the permanent hardness of water be removed?GIve proper chemical equations in support of your answer.

Answer 1

Gan' Permutit method:

In this method, sodium aluminum ortho silicate known as permit or zeolite is used to remove the permanent hardness of the water.

Reaction: ${\mathrm{Na}}_2{\mathrm{Al}}_2{\mathrm{Si}}_2{\mathrm{O}}_8.{\mathrm{KH}}_2\mathrm{O}+{\mathrm{Ca}}^{++}\to 2{\mathrm{Na}}^{+}+\mathrm{CaAl}{2}_2{\mathrm{Si}}_2\mathrm{O}8.{\mathrm{xH}}_2\mathrm{O}$

Calgon' Process"

In this method, sodium-hexa-meta-phosphate (${\left({\mathrm{NaPO}}_3\right)}_6$ known as Calgon is used. The hardness in water is removed by the adsorption of ${\mathrm{Ca}}^{++}$ and ${\mathrm{Mg}}^{++}$ ions.

Ion exchange resin method

In this method, the permanent hardness of water is removed by using resins. ${\mathrm{Ca}}^{++}/{\mathrm{Mg}}^{++}$ ions are exchanged with ${\mathrm{Cl}}^{-}/{\mathrm{SO}}_4^{2-}$ ions are exchanged with anion exchange resin $\left({\mathrm{RNH}}_2\mathrm{OH}\right)$. Demineralized water is formed in this process.

⇒$2\mathrm{RCOOH}+{\mathrm{Ca}}^{++}\to {\left(\mathrm{RCOO}\right)}_2\mathrm{Ca}+2{\mathrm{H}}^{+}$

⇒ ${\mathrm{RNH}}_2\mathrm{OH}+{\mathrm{Cl}}^{-}\to {\mathrm{RNH}}_2\mathrm{Cl}+{\mathrm{OH}}^{-}$

⇒ ${\mathrm{H}}^{+}+{\mathrm{OH}}^{-}\to {\mathrm{H}}_2\mathrm{O}$