Ch.4 - Reactions in Aqueous Solution

Brown - Chemistry: The Central Science 14th Edition

Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232당신이 사용하는 게 아니라요?교과서 변경

Brown 14th Edition

Ch.4 - Reactions in Aqueous Solution

문제 101a

4장, 문제 101a

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?

검증된 단계별 안내

Calculate the moles of Ca^{2+} in the hard water by using the formula: \(\text{moles of }\) Ca^{2+} = \(\text{volume of water (L)}\) \(\times\) \(\text{molarity of }\) Ca^{2+}

Calculate the moles of Mg^{2+} in the hard water by using the formula: \(\text{moles of }\) Mg^{2+} = \(\text{volume of water (L)}\) \(\times\) \(\text{molarity of }\) Mg^{2+}

Determine the total moles of divalent cations (Ca^{2+} and Mg^{2+}) by adding the moles of Ca^{2+} and Mg^{2+}

Since each divalent cation (Ca^{2+} or Mg^{2+}) is replaced by two Na^+ ions to maintain charge balance, calculate the total moles of Na^+ needed by multiplying the total moles of divalent cations by 2

Summarize the calculation to find the total moles of Na^+ required to replace the Ca^{2+} and Mg^{2+} ions in the hard water

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주요 개념

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Ion Concentration and Molarity

Molarity (M) is a measure of concentration defined as the number of moles of solute per liter of solution. In this context, the concentrations of Ca2+ and Mg2+ ions in hard water are given in molarity, which allows us to calculate the total number of moles present in a specific volume of water. Understanding molarity is essential for determining how many moles of Na+ are needed to replace these ions.

Charge Balance in Solutions

Charge balance refers to the principle that in a neutral solution, the total positive charge must equal the total negative charge. In the case of water softening, replacing Ca2+ and Mg2+ (both divalent cations) with Na+ (a monovalent cation) requires careful calculation to ensure that the overall charge remains balanced. This concept is crucial for understanding how to effectively soften water without altering its overall ionic balance.

Stoichiometry in Chemical Reactions

Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced equations. In this scenario, stoichiometric principles are applied to determine the exact number of moles of Na+ needed to replace the moles of Ca2+ and Mg2+ in the hard water. This concept is fundamental for solving problems related to ion exchange and ensuring that the correct amounts of substances are used.

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교과서 질문

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교과서 질문

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