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Q.
Reaction of calgon with hard water containing $Ca^{2+}$ ions produce
TS EAMCET 2017
Solution:
Calgon is a trade name of a complex salt, sodium hexametaphosphate $\left( NaPO _{3}\right)_{6} .$ Calgon ionises to give a complex anion. The addition of calgon to hard water causes the calcium ions of hard water to displace sodium ions from the anion of calgon and form a complex with calgon.
$\left( NaPO _{3}\right)_{6}$ or
$Na _{2}\left( Na _{4} P _{6} O _{18}\right) \longrightarrow 2 Na ^{+}+\underset{\text { (Complex anion)}}{ Na _{4} P _{6} O _{18}^{2-}}$
$ \underset{\text{From hard water }}{Ca ^{2+}}+ \underset{\text{Anion of calgon}}{Na _{4} P _{6} O _{18}^{2-}} \longrightarrow 2 Na ^{+}+ \underset{\text{Goes into solution}}{CaNa _{2} P _{6} O _{18}^{2-}}$