Ch.3 - Molecules and Compounds

Tro - Chemistry: A Molecular Approach 6th Edition

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Tro 6th Edition

Ch.3 - Molecules and Compounds

Problem 123d

Chapter 3, Problem 123d

Determine the chemical formula of each compound and then use it to calculate the mass percent composition of each constituent element. d. cobalt(II) bromide

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Identify the chemical formula of cobalt(II) bromide. Cobalt(II) indicates a +2 charge on cobalt, and bromide has a -1 charge. Therefore, the formula is CoBr₂.

Calculate the molar mass of cobalt(II) bromide. Use the periodic table to find the atomic masses: cobalt (Co) is approximately 58.93 g/mol and bromine (Br) is approximately 79.90 g/mol.

Determine the total molar mass of CoBr₂ by adding the atomic mass of cobalt and twice the atomic mass of bromine: \(58.93 + 2 \times 79.90\).

Calculate the mass percent of cobalt in CoBr₂. Divide the atomic mass of cobalt by the total molar mass of CoBr₂ and multiply by 100 to get the percentage.

Calculate the mass percent of bromine in CoBr₂. Divide the total mass of bromine (2 \(\times\) 79.90) by the total molar mass of CoBr₂ and multiply by 100 to get the percentage.

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Key Concepts

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

Chemical Formula

A chemical formula represents the composition of a compound, indicating the types and numbers of atoms present. For cobalt(II) bromide, the formula is CoBr2, which shows that each formula unit contains one cobalt atom and two bromine atoms. Understanding how to derive the formula from the compound's name is essential for further calculations.

Mass Percent Composition

Mass percent composition is a way to express the relative amounts of each element in a compound as a percentage of the total mass. It is calculated by dividing the mass of each element in one mole of the compound by the molar mass of the compound, then multiplying by 100. This concept is crucial for determining how much of each element contributes to the overall mass of the compound.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all atoms in the chemical formula. For cobalt(II) bromide, the molar mass is essential for calculating the mass percent composition, as it provides the total mass needed for the percentage calculations.

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