Question

The molecular formula of a commercial resin used for exchanging ions in water softening is $C_8{H}_{7}S{O}_{3}Na$ $($molecular weight $206)$. What would be the maximum uptake of $C{a}^{2+}$ ions by the resin when expressed in mole per gram resin?

• A. $\frac{1}{103}$
• B. $\frac{1}{206}$
• C. $\frac{1}{309}$
• D. $\frac{1}{412}$

Answer 1

Answer: (D)

$\frac{1}{412}$

The molecular weight of resin is $206$ g/mol.
$1$ g of resin corresponds to $\frac{1}{206}$ moles.

$1$ mole of calcium ions will displace $2$ moles of sodium ions from resin.

$1$ mole of resin contains $1$ mole of sodium ions and can uptake upto $0.5$ moles of calcium ions.

Hence, $1$ g of resin will uptake $\frac{1}{206}\times 0.5=\frac{1}{412}$ moles of calcium ions.