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Ch.4 - Reactions in Aqueous Solution
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoBrown 14th EditionCh.4 - Reactions in Aqueous SolutionProblema 101b
Capitolo 4, Problema 101b

Hard water contains Ca2+, Mg2+, and Fe2+, which interfere with the action of soap and leave an insoluble coating on the insides of containers and pipes when heated. Water softeners replace these ions with Na+. Keep in mind that charge balance must be maintained. (b) If the sodium is added to the water softener in the form of NaCl, how many grams of sodium chloride are needed?

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1
Identify the ions in hard water that need to be replaced: \( \text{Ca}^{2+}, \text{Mg}^{2+}, \text{Fe}^{2+} \).
Understand that each \( \text{Ca}^{2+}, \text{Mg}^{2+}, \text{Fe}^{2+} \) ion is replaced by two \( \text{Na}^+ \) ions to maintain charge balance.
Determine the total moles of \( \text{Ca}^{2+}, \text{Mg}^{2+}, \text{Fe}^{2+} \) ions present in the water.
Calculate the moles of \( \text{Na}^+ \) ions needed, which is twice the moles of \( \text{Ca}^{2+}, \text{Mg}^{2+}, \text{Fe}^{2+} \) ions.
Use the molar mass of NaCl to convert the moles of \( \text{Na}^+ \) ions to grams of NaCl needed.

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Ion Exchange

Ion exchange is a process where undesirable ions in water, such as Ca²⁺ and Mg²⁺, are replaced with more desirable ions, typically Na⁺ from sodium chloride (NaCl). This process is crucial in water softening, as it reduces the hardness of water, allowing soap to lather more effectively and preventing scale buildup in pipes.
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Ion Formation

Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions. In the context of the question, it is used to determine the amount of NaCl needed to replace the hard water ions while maintaining charge balance. Understanding stoichiometric relationships is essential for accurately calculating the required mass of sodium chloride.
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Stoichiometry Concept

Charge Balance

Charge balance refers to the principle that the total positive charge must equal the total negative charge in a solution. In the case of water softening, when replacing Ca²⁺ and Mg²⁺ ions with Na⁺ ions, it is important to ensure that the overall charge remains neutral. This concept is vital for understanding how many moles of Na⁺ are needed to replace the divalent cations.
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Formal Charge
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Hard water contains Ca2+, Mg2+, and Fe2+, which interfere with the action of soap and leave an insoluble coating on the insides of containers and pipes when heated. Water softeners replace these ions with Na+. Keep in mind that charge balance must be maintained. (a) If 1500 L of hard water contains 0.020 M Ca2+ and 0.0040 M Mg2+, how many moles of Na+ are needed to replace these ions?

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