Ch.3 - Molecules, Compounds & Chemical Equations

Problem 88c

Chapter 3, Problem 88c

A chemist decomposes samples of several compounds; the masses of their constituent elements are listed. Calculate the empirical formula for each compound. c. 2.128 g Be, 7.557 g S, 15.107 g O

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Determine the number of moles of each element by dividing the mass of each element by its molar mass.

For beryllium (Be), use its molar mass of approximately 9.01 g/mol.

For sulfur (S), use its molar mass of approximately 32.07 g/mol.

For oxygen (O), use its molar mass of approximately 16.00 g/mol.

Divide the number of moles of each element by the smallest number of moles calculated to find the simplest whole number ratio.

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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 of each element in a sample, which is converted to moles, allowing for the determination of the ratio of the elements. This formula does not provide information about the actual number of atoms in a molecule but rather the relative proportions.

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 calculate the empirical formula, the mass of each element is converted to moles using the molar mass, which allows for the comparison of the amounts of different elements in the sample.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). Each element has a specific molar mass, which can be found on the periodic table. In the context of calculating empirical formulas, the molar mass is used to convert the mass of each element in the sample to moles, facilitating the determination of the simplest ratio of the elements.

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