Question

When zeolite is treated with hard water, the sodium ions are exchanged with:

• A. ${OH}^{-}$ ions
• B. $S{O}_4^{2-}$ions
• C. $C{a}^{2+}$ ions
• D. $H^{+}$ ions

Answer 1

The correct option is C

$C{a}^{2+}$ ions

Hard water contains dissolved salts of chlorides, sulphates and bicarbonates of calcium and magnesium. When zeolite (hydrated sodium aluminium silicate) is treated with hard water, the sodium ions are exchanged with ${\text{Ca}}^{2+}$ and ${\text{Mg}}^{2+}$ ions hence making water soft. The reaction occurs as follows:

${\text{Na}}_2{\text{Al}}_2{\text{Si}}_2{\text{O}}_8.{\text{xH}}_2\text{O}+{\text{Ca}}^{2+}\to {\text{CaAl}}_2{\text{Si}}_2{\text{O}}_8.{\text{xH}}_2\text{O}+{2\text{Na}}^{+}$