(d) If 45.3 mL of a 0.108 M HCl solution is needed to neutralize a solution of KOH, how many grams of KOH must be present in the solution?
Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 82c
(c) If 55.8 mL of a BaCl2 solution is needed to precipitate all the sulfate ion in a 752-mg sample of Na2SO4, what is the molarity of the BaCl2 solution?

1
Identify the chemical reaction: BaCl_2 + Na_2SO_4 \rightarrow BaSO_4 + 2NaCl.
Calculate the moles of Na_2SO_4 using its molar mass: \text{moles of Na}_2\text{SO}_4 = \frac{\text{mass of Na}_2\text{SO}_4}{\text{molar mass of Na}_2\text{SO}_4}.
Use the stoichiometry of the balanced equation to find the moles of BaCl_2 needed: \text{moles of BaCl}_2 = \text{moles of Na}_2\text{SO}_4.
Convert the volume of BaCl_2 solution from mL to L: \text{volume in L} = \frac{55.8 \text{ mL}}{1000}.
Calculate the molarity of the BaCl_2 solution: \text{Molarity} = \frac{\text{moles of BaCl}_2}{\text{volume of solution in L}}.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Stoichiometry
Stoichiometry is the calculation of reactants and products in chemical reactions. It involves using balanced chemical equations to determine the relationships between the amounts of substances consumed and produced. In this question, stoichiometry is essential to relate the moles of BaCl2 used to the moles of sulfate ions from Na2SO4 that are being precipitated.
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Molarity
Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in units of moles per liter (mol/L). To find the molarity of the BaCl2 solution in this problem, one must calculate the moles of BaCl2 that reacted and divide that by the volume of the solution in liters.
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Precipitation Reactions
Precipitation reactions occur when two soluble salts react to form an insoluble product, known as a precipitate. In this case, BaCl2 reacts with Na2SO4 to form barium sulfate (BaSO4), which precipitates out of solution. Understanding this concept is crucial for determining how much BaCl2 is needed to completely react with the sulfate ions present in the sample.
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Related Practice
Textbook Question
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(a) How many milliliters of 0.120 M HCl are needed to completely neutralize 50.0 mL of 0.101 M Ba(OH)2 solution?
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(b) How many milliliters of 0.125 M H2SO4 are needed to neutralize 0.200 g of NaOH?
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(d) If 42.7 mL of 0.208 M HCl solution is needed to neutralize a solution of Ca(OH)2, how many grams of Ca(OH)2 must be in the solution?
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The distinctive odor of vinegar is due to acetic acid, CH3COOH, which reacts with sodium hydroxide according to: CH3COOH1aq2 + NaOH1aq2¡ H2O1l2 + NaCH3COO1aq2 If 3.45 mL of vinegar needs 42.5 mL of 0.115 M NaOH to reach the equivalence point in a titration, how many grams of acetic acid are in a 1.00-qt sample of this vinegar?
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