Ch.3 - Chemical Reactions and Reaction Stoichiometry

Brown - Chemistry: The Central Science 14th Edition

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Brown 14th Edition

Ch.3 - Chemical Reactions and Reaction Stoichiometry

Problem 47b,c

Chapter 3, Problem 47b,c

Determine the empirical formulas of the compounds with the following compositions by mass: (b) 57.5% Na, 40.0% O, and 2.5% H (c) 41.1% N, 11.8% H, and the remainder S

Verified step by step guidance

Convert the percentage of each element to grams, assuming you have 100 grams of the compound. This means you have 57.5 grams of Na, 40.0 grams of O, and 2.5 grams of H.

Convert the mass of each element to moles by dividing by their respective molar masses: Na (22.99 g/mol), O (16.00 g/mol), and H (1.01 g/mol).

Determine the mole ratio of the elements by dividing each element's mole value by the smallest number of moles calculated in the previous step.

If necessary, multiply the mole ratios by a whole number to get whole numbers for each element in the compound.

Write the empirical formula using the whole number mole ratios as subscripts for each element.

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Key Concepts

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

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 percentages of each element, which are converted to moles and then simplified to the lowest ratio. This formula does not provide information about the actual number of atoms in a molecule but rather the relative proportions of each element.

Mole Concept

The mole is a fundamental unit in chemistry that quantifies the amount of substance. One mole corresponds to Avogadro's number, approximately 6.022 x 10²³ entities (atoms, molecules, etc.). To determine the empirical formula, the mass percentages of elements are converted to moles by dividing by their respective atomic masses, allowing for the comparison of the number of moles of each element.

Mass Percent Composition

Mass percent composition refers to the percentage by mass of each element in a compound. It is calculated by dividing the mass of each element in a sample by the total mass of the sample and multiplying by 100. This information is crucial for determining the empirical formula, as it provides the starting point for converting mass to moles and establishing the ratios of the elements.

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