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Ch.3 - Molecules, Compounds & Chemical Equations
Tro - Chemistry: A Molecular Approach 4th Edition
Tro4th EditionChemistry: A Molecular ApproachISBN: 9780134112831Not the one you use?Change textbook
All textbooksTro 4th EditionCh.3 - Molecules, Compounds & Chemical EquationsProblem 123a,b
Chapter 3, Problem 123a,b

Determine the chemical formula of each compound and then use it to calculate the mass percent composition of each constituent element. a. potassium chromate b. lead(II) phosphate

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1
Identify the chemical formula for lead(II) phosphate. Lead(II) is represented as Pb^{2+} and phosphate is represented as PO_4^{3-}.
Balance the charges to determine the correct formula. To balance the charges, you need three Pb^{2+} ions to balance with two PO_4^{3-} ions, resulting in the formula Pb_3(PO_4)_2.
Calculate the molar mass of the compound Pb_3(PO_4)_2 by adding the atomic masses of all atoms in the formula. Use the periodic table to find the atomic masses: Pb, P, and O.
Determine the mass of each element in one mole of the compound. Multiply the number of each type of atom by its atomic mass.
Calculate the mass percent composition of each element by dividing the total mass of each element by the molar mass of the compound and multiplying by 100%.

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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 example, lead(II) phosphate is represented as Pb3(PO4)2, where 'Pb' stands for lead, 'P' for phosphorus, and 'O' for oxygen. Understanding how to derive the formula from the compound's name is essential for further calculations.
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Mass Percent Composition

Mass percent composition is a way to express the relative amount 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. Knowing the molar mass is vital for converting between grams and moles, which is necessary for calculating mass percent composition.
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