Ch.3 - Chemical Reactions and Reaction Stoichiometry

Problem 93

Chapter 3, Problem 93

Vanillin, the dominant flavoring in vanilla, contains C, H, and O. When 1.05 g of this substance is completely combusted, 2.43 g of CO2 and 0.50 g of H2O are produced. What is the empirical formula of vanillin?

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Determine the moles of carbon in CO2 by using the molar mass of CO2 (44.01 g/mol) and the fact that each mole of CO2 contains one mole of carbon.

Calculate the moles of hydrogen in H2O by using the molar mass of H2O (18.02 g/mol) and the fact that each mole of H2O contains two moles of hydrogen.

Find the mass of carbon and hydrogen in the original sample by multiplying the moles of each element by their respective atomic masses (C: 12.01 g/mol, H: 1.008 g/mol).

Subtract the mass of carbon and hydrogen from the total mass of the sample to find the mass of oxygen.

Convert the mass of oxygen to moles using the atomic mass of oxygen (16.00 g/mol), then determine the simplest whole number ratio of moles of C, H, and O to find the empirical formula.

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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. During this process, a sample is burned in excess oxygen, producing carbon dioxide (CO2) and water (H2O). The masses of these products are measured to infer the amounts of carbon and hydrogen in the original compound, which is essential for deriving its empirical formula.

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 moles of each element calculated from the mass of products obtained during combustion. This formula provides insight into the basic composition of the substance, although it may not reflect the actual molecular structure.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It involves using balanced chemical equations to calculate the amounts of substances consumed and produced. In the context of combustion analysis, stoichiometry helps convert the masses of CO2 and H2O into moles of carbon and hydrogen, which are crucial for determining the empirical formula.

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