The molecular formula of a commercial resin used for exchanging ions in water softening is $\mathrm{C}_{8} \mathrm{H}_{7} \mathrm{SO}_{3} \mathrm{Na}$ (Mol. Wt. 206). What would be the maximum uptake of $\mathrm{Ca}^{2+}$ ions by the resin when expressed in mole per gram resin?

JEE Main · 2015 · 04 Apr 2015 · Offline · Hydrogen

The molecular formula of a commercial resin used for exchanging ions in water softening is

C_{8} H_{7} SO_{3} Na

(Mol. Wt. 206). What would be the maximum uptake of

Ca^{2 +}

ions by the resin when expressed in mole per gram resin?

Answer: (C)

The resin swaps sodium for calcium, and because

C a^{2 +}

carries two charges it takes two

Na

sites to capture one calcium ion:

2 C_{8} H_{7} S O_{3} Na + C a^{2 +} \to (C_{8} H_{7} S O_{3})_{2} Ca + 2 N a^{+}

. So one mole of

C a^{2 +}

needs two moles of resin, i.e.

2 \times 206 = 412

g. The maximum uptake is therefore

\frac{1}{412}

mole of

C a^{2 +}

per gram of resin.

JEE Main · 2015 · 04 Apr 2015 · Offline · Single correct option