Ch.4 - Reactions in Aqueous Solution

Problem 149a

Chapter 4, Problem 149a

Compound X contains only the elements C, H, O, and S. A 5.00 g sample undergoes complete combustion to give 4.83 g of CO₂, 1.48 g of H₂O, and a certain amount of SO₂ that is further oxidized to SO3 and dissolved in water to form sulfuric acid, H₂SO₄. On titration of the H₂SO₄, 109.8 mL of 1.00 M NaOH is needed for complete reaction. (Both H atoms in sulfuric acid are acidic and react with NaOH.) (a) What is the empirical formula of X?

Verified step by step guidance

Calculate the moles of CO2 produced using its molar mass.

Determine the moles of carbon in the sample from the moles of CO2.

Calculate the moles of H2O produced using its molar mass.

Determine the moles of hydrogen in the sample from the moles of H2O.

Calculate the moles of sulfur in the sample using the volume and molarity of NaOH, considering the stoichiometry of the reaction with H2SO4.

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Key Concepts

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

Combustion Analysis

Combustion analysis is a technique used to determine the elemental composition of organic compounds. In this process, a sample is burned in excess oxygen, producing CO2 and H2O, which can be measured to calculate the amounts of carbon and hydrogen in the original compound. The mass of sulfur can also be determined from the products formed, such as SO2 and subsequently SO3.

Empirical Formula

The empirical formula of a compound represents the simplest whole-number ratio of the elements present in that compound. To determine the empirical formula, the moles of each element are calculated from the mass of the combustion products, and then these values are simplified to the smallest whole numbers. This formula provides insight into the basic composition of the compound without indicating the actual number of atoms in a molecule.

Titration and Stoichiometry

Titration is a quantitative analytical method used to determine the concentration of a solute in a solution. In this case, sulfuric acid (H2SO4) is titrated with sodium hydroxide (NaOH), where the volume and molarity of NaOH used allow for the calculation of the moles of H2SO4 present. Understanding the stoichiometry of the reaction is crucial, as it reveals the mole ratio between the acid and the base, which is essential for determining the amount of sulfur in the original compound.

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Textbook Question

Iron content in ores can be determined by a redox procedure in which the sample is first reduced with Sn2+, as in Problem 4.130, and then titrated with KMnO4 to oxidize the Fe2+ to Fe3+. The balanced equation is What is the mass percent Fe in a 2.368 g sample if 48.39 mL of a 0.1116 M KMnO4 solution is needed to titrate the Fe3 + ?

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Textbook Question

A mixture of FeCl2 and NaCl is dissolved in water, and addi-tion of aqueous silver nitrate then yields 7.0149 g of a pre-cipitate. When an identical amount of the mixture is titrated with MnO4 -, 14.28 mL of 0.198 M KMnO4 is needed for complete reaction. What are the mass percents of the two compounds in the mixture? (Na+ and Cl-do not react with MnO4 -. The equation for the reaction of Fe2+ with MnO4 was given in Problem 4.146.)

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Textbook Question

Salicylic acid, used in the manufacture of aspirin, contains only the elements C, H, and O and has only one acidic hydrogen that reacts with NaOH. When 1.00 g of salicylic acid undergoes complete combustion, 2.23 g CO2 and 0.39 g H2O are obtained. When 1.00 g of salicylic acid is titrated with 0.100 M NaOH, 72.4 mL of base is needed for complete reaction. What are the empirical and molecular formulas of salicylic acid?

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Textbook Question

(b) When 5.00 g of X is titrated with NaOH, it is found that X has two acidic hydrogens that react with NaOH and that 54.9 mL of 1.00 M NaOH is required to completely neu-tralize the sample. What is the molecular formula of X?

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Textbook Question

A 1.268 g sample of a metal carbonate (MCO3) was treated with 100.00 mL of 0.1083 M sulfuric acid (H2SO4), yielding CO2 gas and an aqueous solution of the metal sulfate (MSO4). The solution was boiled to remove all the dissolved CO2 and was then titrated with 0.1241 M NaOH. A 71.02 mL volume of NaOH was required to neutralize the excess H2SO4. (a) What is the identity of the metal M?

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Textbook Question

(b) How many liters of CO2 gas were produced if the density of CO2 is 1.799 g/L?

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