Answer:
16 moles of Na^+ is needed to replace Ca^2+ and Fe^3+.
Explanation:
Number of moles ions is given by concentration of ions multiplied by volume of hard water.
Concentration of Ca^2+ = 0.015 M
Concentration of Fe^3+ = 0.001 M
Volume of hard = 1×10^3 L
Number of moles of Ca^2+ = 0.015 × 1×10^3 = 15 moles
Number of moles of Fe^3+ = 0.001 × 1×10^3 = 1 mole
Number of moles of Na^+ needed to replace these ions = 15 + 1 = 16 moles.
