Question

Which of the following compounds is used for water softening?

• A. $C{a}_3(P{O}_4{)}_2$
• B. $N{a}_{3}P{O}_4$
• C. $N{a}_6{P}_6{O}_{18}$
• D. $N{a}_{2}HP{O}_4$

Answer 1

Answer: (C)

$N{a}_6{P}_6{O}_{18}$

Sodium hexametaphosphate $\left(N{a}_6{P}_6{O}_{18}\right),$ commercially called 'calgon' is used for water softening. Calgon reacts with salts of $Ca/Mg$ (present in hard water) and forms inactive complex anions that do not precipitate in soap solution.