Question

What is Calgon?

• A. potassium Phantom metaphosphate
• B. sodium penta metaphosphate
• C. potassium hexametaphosphate
• D. sodium hexametaphosphate

Answer 1

The correct option is D sodium hexametaphosphate

Calgon is the trade name for complex salt, Sodium hexametaphosphate $(NaP{O}_3{)}_6$. This method is used for softening the hard water.
In this process, calgon ionise in water to form complex anion and $N{a}^{+}$ ions. The $M{g}^{+2}$ and $C{a}^{+2}$ ion in water will displace the $N{a}^{+}$ ion from complex anion and they form a soluble complex compound. They doesn't get precipitated.
This results in the removal of hardness from water and sodium ion from calgon is released into water.

$N{a}_6{P}_6{O}_{18}\to 2N{a}^{+}+N{a}_4{P}_6{O}_{18}^{2-}$
$M^{2+}+N{a}_4{P}_6{O}_{18}^{2-}\to [N{a}_{2}M{P}_6{O}_{18}{]}^{2-}+2N{a}^{+}$
Where, M = Mg and Ca