Ch.4 - Reactions in Aqueous Solution

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.4 - Reactions in Aqueous Solution

Problem 132

Chapter 4, Problem 132

Alcohol levels in blood can be determined by a redox reaction with potassium dichromate according to the balanced equation What is the blood alcohol level in mass percent if 8.76 mL of 0.049 88 M K2Cr2O7 is required for complete reaction with a 10.002 g sample of blood?

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Identify the balanced chemical equation for the reaction between ethanol (C2H5OH) and potassium dichromate (K2Cr2O7).

Calculate the moles of K2Cr2O7 used in the reaction using the formula: moles = concentration (M) \(\times\) volume (L).

Use the stoichiometry of the balanced equation to determine the moles of ethanol (C2H5OH) that reacted.

Convert the moles of ethanol to mass using the molar mass of ethanol.

Calculate the mass percent of ethanol in the blood sample using the formula: (mass of ethanol / mass of blood sample) \(\times\) 100%.

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Key Concepts

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

Redox Reactions

Redox reactions involve the transfer of electrons between two species, resulting in oxidation and reduction processes. In this context, potassium dichromate (K2Cr2O7) acts as an oxidizing agent, facilitating the oxidation of alcohol in the blood. Understanding how to identify the oxidized and reduced species is crucial for analyzing the reaction and calculating the blood alcohol level.

Molarity and Stoichiometry

Molarity (M) is a measure of concentration defined as moles of solute per liter of solution. In this question, the molarity of K2Cr2O7 is essential for determining the number of moles reacting with the blood sample. Stoichiometry allows us to relate the moles of reactants to the moles of products, enabling the calculation of the blood alcohol level based on the balanced chemical equation.

Mass Percent Concentration

Mass percent concentration is a way to express the concentration of a component in a mixture, calculated as the mass of the solute divided by the total mass of the solution, multiplied by 100. In this scenario, determining the blood alcohol level in mass percent requires converting the moles of alcohol oxidized into mass and then relating it to the mass of the blood sample to find the final concentration.

Related Practice

Textbook Question

Calcium levels in blood can be determined by adding oxa-late ion to precipitate calcium oxalate, CaC2O4, followed by dissolving the precipitate in aqueous acid and titrating the resulting oxalic acid (H2C2O4) with KMnO4: How many milligrams of Ca2+ are present in 10.0 mL of blood if 21.08 mL of 0.000 988 M KMnO4 solution is needed for the titration?

Standardized solutions of KBrO3 are frequently used in redox titrations. The necessary solution can be made by dissolving KBrO3 in water and then titrating it with an As(III) solution. What is the molar concentration of a KBrO3 solution if 28.55 mL of the solution is needed to titrate 1.550 g of As2O3? See Problem 4.128 for the balanced equation. (As2O3 dissolves in aqueous acid solution to yield H3AsO3: As2O3 + 3 H2OS 2 H3AsO3.)

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Textbook Question

A volume of 18.72 mL of 0.1500 M K2Cr2O7 solution was required to titrate a sample of FeSO4 according to the equation in Problem 4.126. What is the mass of the sample?

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Textbook Question

The concentration of the Sn2+ solution used in Problem 4.130 can be found by letting it react with a known amount of Fe2+. What is the molar concentration of an Sn2+ solution if 23.84 mL is required for complete reaction with 1.4855 g of Fe2O3?

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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

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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