A commercial synthetic cation exchange resin used for water softening has the general molecular form — Hydrogen Chemistry Question
Question
A commercial synthetic cation exchange resin used for water softening has the general molecular formula $C_8H_7SO_3Na$ (Molar mass = $206\text{ g mol}^{-1}$). Assuming maximum theoretical efficiency, what is the exact mass (in grams) of this specific resin required to completely uptake $1\text{ mole}$ of $Ca^{2+}$ ions from a hard water supply?
Answer: 412
💡 Solution & Explanation
The stoichiometry of the ion exchange reaction is: $2(C_8H_7SO_3Na) + Ca^{2+} \rightarrow (C_8H_7SO_3)_2Ca + 2Na^+$. It requires $2\text{ moles}$ of the sodium resin to exchange $1\text{ mole}$ of $Ca^{2+}$. The mass required is $2\text{ moles} \times 206\text{ g mol}^{-1} = 412\text{ grams}$.
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