Question

Hard water when passed through ion exchanger containing resin $RS{O}_{3}Na$ group becomes free from:

• A. $C{l}^{-}$
• B. $S{O}_4^{2-}$
• C. $H_3{O}^{+}$
• D. $C{a}^{2+}$

Answer 1

The correct option is D $C{a}^{2+}$

Nowadays hard water is softened by using synthetic cation exchanger. The resin exchanges the $N{a}^{+}$ ion with $C{a}^{2+}$ and $M{g}^{2+}$ ions that are present in hard water to make the water soft. Here $R^{\prime }=RS{O}_3^{-}$ is resin anion.
$2R^{\prime }Na\left(s\right)+M^{2+}\left(aq\right)\to R_2^{\prime }M\left(s\right)+2N{a}^{+}\left(aq\right)$
The resin can be regenerated by adding aqueous $NaCl$ solution.