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Ch.3 - Chemical Reactions and Reaction Stoichiometry
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.3 - Chemical Reactions and Reaction StoichiometryProblem 55a
Chapter 3, Problem 55a

(a) Combustion analysis of toluene, a common organic solvent, gives 5.86 mg of CO2 and 1.37 mg of H2O. If the compound contains only carbon and hydrogen, what is its empirical formula?

Verified step by step guidance
1
Convert the mass of CO2 to moles of carbon: Use the molar mass of CO2 (44.01 g/mol) to find the moles of CO2, then use the ratio of carbon in CO2 (1 mole of C per mole of CO2) to find the moles of carbon.
Convert the mass of H2O to moles of hydrogen: Use the molar mass of H2O (18.02 g/mol) to find the moles of H2O, then use the ratio of hydrogen in H2O (2 moles of H per mole of H2O) to find the moles of hydrogen.
Determine the simplest whole number ratio of moles of carbon to moles of hydrogen: Divide the moles of each element by the smallest number of moles calculated in the previous steps.
Write the empirical formula: Use the whole number ratio from the previous step to write the empirical formula of the compound.
Verify the empirical formula: Ensure that the empirical formula is consistent with the given data and the assumption that the compound contains only carbon and hydrogen.

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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 composition of organic compounds by burning them in excess oxygen. The products of combustion, typically carbon dioxide (CO2) and water (H2O), are measured to calculate the amounts of carbon and hydrogen in the original compound. This method is essential for deriving empirical formulas, as it provides the necessary data to relate the mass of the products back to the elements in the compound.
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Combustion of Non-Hydrocarbons

Empirical Formula

The empirical formula of a compound represents the simplest whole-number ratio of the elements present in that compound. It is derived from the mass of each element obtained from combustion analysis and is crucial for understanding the basic composition of the substance. For example, if a compound contains carbon and hydrogen, the empirical formula will indicate the ratio of carbon atoms to hydrogen atoms, which can be determined from the moles of each element calculated from their respective masses.
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Mole Concept

The mole concept is a fundamental principle in chemistry that relates the mass of a substance to the number of particles (atoms, molecules, etc.) it contains. One mole of any substance contains Avogadro's number of entities, approximately 6.022 x 10^23. In combustion analysis, converting the mass of CO2 and H2O produced into moles allows for the determination of the moles of carbon and hydrogen in the original compound, which is essential for calculating the empirical formula.
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Related Practice
Textbook Question

Valproic acid, used to treat seizures and bipolar disorder, is composed of C, H, and O. A 0.165-g sample is combusted to produce 0.166 g of water and 0.403 g of carbon dioxide. What is the empirical formula for valproic acid?

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Textbook Question

(a) The characteristic odor of pineapple is due to ethyl butyrate, a compound containing carbon, hydrogen, and oxygen. Combustion of 2.78 mg of ethyl butyrate produces 6.32 mg of CO2 and 2.58 mg of H2O. What is the empirical formula of the compound?

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Textbook Question

Determine the empirical and molecular formulas of each of the following substances: (a) Ibuprofen, a headache remedy, contains 75.69% C, 8.80% H, and 15.51% O by mass and has a molar mass of 206 g/mol.

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Textbook Question

Determine the empirical and molecular formulas of each of the following substances: (c) Monosodium glutamate (MSG), a flavor enhancer in certain foods, contains 35.51% C, 4.77% H, 37.85% O, 8.29% N, and 13.60% Na, and has a molar mass of 169 g/mol.

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Textbook Question

(b) Menthol, the substance we can smell in mentholated cough drops, is composed of C, H, and O. A 0.1005-g sample of menthol is combusted, producing 0.2829 g of CO2 and 0.1159 g of H2O. What is the empirical formula for menthol? If menthol has a molar mass of 156 g/mol, what is its molecular formula?

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Textbook Question

Determine the empirical and molecular formulas of each of the following substances: (b) Cadaverine, a foul-smelling substance produced by the action of bacteria on meat, contains 58.55% C, 13.81% H, and 27.40% N by mass; its molar mass is 102.2 g/mol.

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