Hard water contains Ca 2+ , Mg 2+ , and Fe 2+ ions, which interfere with the act

Question

Hard water contains Ca 2+, Mg2+, and Fe2+ ions, which interfere with the action of soap and leave an insoluble precipitate solid coating on the insides of containers, tubs, and pipes when heated. Water softeners replace these ions with Na+ ions. If 1500.00 L of hard water contains 0.200M of Ca2+, 0.00400M of Mg2+, and 0.0700M of Fe2+, how much salt (mass) in the form of sodium chloride tablets will be needed in the water softener to counter-act the hardness? Write complete ion equations and setup of course.

Explanation / Answer

No. of moles of Ca2+ = 0.2 * 1500 = 300
No. of moles of Mg2+ = 0.004 * 1500 = 6
No. of moles of Fe2+ = 0.07 * 1500 = 105

2NaCL + Ca2+ -> CaCl2 + 2Na+
2NaCL + Mg2+ -> MgCl2 + 2Na+
2NaCL + Fe2+ -> FeCl2 + 2Na+

Thus, 1 mole of Ca2+, Mg2+, Fe2+ require 2 moles of NaCL each.

Thus, total moles of NaCL = 2 * (300 + 6 + 105) = 822 moles

Mass of NaCL = 822 * 58.5 g = 48087 g = 48.087 kg

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