Question

Permanent hardness of water can be removed by adding calgon $(NaP{O}_3{)}_6$. This is an example of:

• A. Adsorption
• B. Exchange of ions
• C. Precipitation
• D. None of these

Answer 1

The correct option is B Exchange of ions

Calgon ($N{a}_6{P}_6{O}_{18}$) ionizes to give a complex anion. The addition of calgon to hard water causes the calcium and magnesium ions from hard water to displace the sodium ion from the anion of Calgon.
$N{a}_2\left[N{a}_4\right(P{O}_3{)}_6]+2C{a}^{2+}\to N{a}_2[C{a}_2\left(P{O}_3{)}_6\right]+4N{a}^{+}$