Ch.4 - Reactions in Aqueous Solution

Problem 150a

Chapter 4, Problem 150a

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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Determine the moles of H2SO4 initially added to the reaction by using the concentration and volume of the sulfuric acid solution. Use the formula: Moles = Molarity × Volume (in liters).

Calculate the moles of NaOH used in the titration using its molarity and the volume used. Again, use the formula: Moles = Molarity × Volume (in liters).

Since NaOH neutralizes the excess H2SO4, calculate the moles of H2SO4 that reacted with the metal carbonate by subtracting the moles of NaOH from the moles of H2SO4 initially added.

Write the balanced chemical equation for the reaction between the metal carbonate (MCO3) and sulfuric acid (H2SO4) to form metal sulfate (MSO4), water (H2O), and carbon dioxide (CO2). From the stoichiometry of the reaction, determine the moles of MCO3 that reacted.

Calculate the molar mass of the metal carbonate (MCO3) using the mass of the sample and the moles of MCO3. Then, subtract the molar mass of CO3 (60.01 g/mol) from the molar mass of MCO3 to find the atomic mass of the metal M, which helps identify the metal.

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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 based on the balanced chemical equation. It allows us to determine the relationships between the quantities of substances involved in a reaction. In this question, stoichiometry is essential for relating the amount of sulfuric acid used to the amount of metal carbonate that reacted, ultimately helping to identify the metal.

Acid-Base Reactions

Acid-base reactions involve the transfer of protons (H+) between reactants, typically resulting in the formation of water and a salt. In this scenario, sulfuric acid reacts with the metal carbonate to produce carbon dioxide and a metal sulfate. Understanding the nature of these reactions is crucial for determining how much acid was neutralized by the base, which is key to identifying the metal.

Titration

Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. It involves the gradual addition of a titrant to a solution until a reaction reaches completion, indicated by a color change or pH change. In this question, the titration of the remaining sulfuric acid with NaOH provides critical data to calculate the amount of acid that reacted, which is necessary for identifying the metal in the carbonate.

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Acid-Base Titration

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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

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?

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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

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

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Textbook Question

Element M is prepared industrially by a two-step procedure according to the following (unbalanced) equations:

Assume that 0.855 g of M₂O₃ is submitted to the reaction sequence. When the HCl produced in step (2) is dissolved in water and titrated with 0.511 M NaOH, 144.2 mL of the NaOH solution is required to neutralize the HCl. (a) Balance both equations.

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Textbook Question

Assume that you dissolve 10.0 g of a mixture of NaOH and Ba(OH)2 in 250.0 mL of water and titrate with 1.50 M hydrochloric acid. The titration is complete after 108.9 mL of the acid has been added. What is the mass in grams of each substance in the mixture?

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