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Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 136

A procedure for determining the amount of iron in a sample is to convert the iron to Fe2+ and then titrate it with a solu-tion of Ce(NH4)2(NO3)6: What is the mass percent of iron in a sample if 1.2284 g of the sample requires 54.91 mL of 0.1018 M Ce(NH4)2(NO3)6 for complete reaction?

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Titration

Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. In this process, a solution of known concentration (the titrant) is gradually added to a solution of unknown concentration until the reaction reaches its endpoint, indicated by a color change or other measurable signal. This method is essential for calculating the amount of a specific substance, such as iron in this case, based on the volume and concentration of the titrant used.
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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 moles per liter (mol/L) and is crucial for stoichiometric calculations in titrations. In the given problem, the molarity of the cerium solution (0.1018 M) is used to determine how many moles of cerium react with the iron, allowing for the calculation of the mass percent of iron in the sample.
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Mass Percent

Mass percent is a way of expressing the concentration of a component in a mixture, calculated as the mass of the component divided by the total mass of the mixture, multiplied by 100. This concept is important for determining the proportion of iron in the sample after the titration, as it provides a clear understanding of how much of the sample's mass is attributable to iron, which is essential for evaluating the sample's quality or compliance with specifications.
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Related Practice
Textbook Question
Assume that you have 1.00 g of a mixture of benzoic acid (Mol. wt. = 122) and gallic acid (Mol. wt. = 170)), both of which contain one acidic hydrogen that reacts with NaOH. On titrating the mixture with 0.500 M NaOH, 14.7 mL of base is needed to completely react with both acids. What mass in grams of each acid is present in the original mixture?
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Textbook Question

A compound with the formula XOCl2 reacts with water, yielding HCl and another acid H2XO3, which has two acidic hydrogens that react with NaOH. When 0.350 g of XOCl2 was added to 50.0 mL of water and the resultant solution was titrated, 96.1 mL of 0.1225 M NaOH was required to react with all the acid. (a) Write a balanced equation for the reaction of XOCl2 with H2O.

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Textbook Question

A compound with the formula XOCl2 reacts with water, yielding HCl and another acid H2XO3, which has two acidic hydrogens that react with NaOH. When 0.350 g of XOCl2 was added to 50.0 mL of water and the resultant solution was titrated, 96.1 mL of 0.1225 M NaOH was required to react with all the acid. (b) What are the atomic mass and identity of element X?

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Textbook Question

Some metals occur naturally in their elemental state while others occur as compounds in ores. Gold, for instance, is found as the free metal; mercury is obtained by heating mercury(II) sulfide ore in oxygen; and zinc is obtained by heating zinc(II) oxide ore with coke (carbon). Judging from their positions in the activity series, which of the metals sil-ver, platinum, and chromium would probably be obtained by (a) finding it in its elemental state?

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Textbook Question

Some metals occur naturally in their elemental state while others occur as compounds in ores. Gold, for instance, is found as the free metal; mercury is obtained by heating mercury(II) sulfide ore in oxygen; and zinc is obtained by heating zinc(II) oxide ore with coke (carbon). Judging from their positions in the activity series, which of the metals sil-ver, platinum, and chromium would probably be obtained by (c) heating its oxide with coke?

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Textbook Question
A sample weighing 14.98 g and containing a small amount of copper was treated to give a solution containing aque-ous Cu2+ ions. Sodium iodide was then added to yield solid copper(I) iodide plus I3 with thiosulfate, S2O3 - ion, and the I3 - was titrated 2-. The titration required 10.49 mL of 0.100 M Na2S2O3 for complete reaction. What is the mass percent copper in the sample? The balanced equations are
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