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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 139
Chapter 3, Problem 139

The chloride of an unknown metal is believed to have the formula MCl3. A 2.395-g sample of the compound contains 3.606×10-2 mol Cl. Find the atomic mass of M.

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1
Determine the moles of metal chloride in the sample. Since the formula of the metal chloride is MCl3, which means each mole of MCl3 contains 3 moles of Cl. Use the given moles of Cl to find the moles of MCl3 by dividing the moles of Cl by 3.
Calculate the molar mass of MCl3. Since you know the mass of the MCl3 sample and the moles of MCl3, use the formula: Molar mass = Mass of the sample / Moles of MCl3.
Write the formula for the molar mass of MCl3 in terms of the atomic mass of M (M_m) and the molar mass of Cl (Cl_m). The formula is Molar mass of MCl3 = M_m + 3 * Cl_m.
Set up the equation from step 2 equal to the expression from step 3. This will allow you to solve for the atomic mass of M (M_m).
Solve the equation for M_m (the atomic mass of M) by isolating M_m on one side of the equation.

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Key Concepts

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

Molar Mass and Moles

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). The number of moles of a substance can be calculated using the formula: moles = mass (g) / molar mass (g/mol). In this question, understanding how to convert between mass and moles is essential for determining the atomic mass of the unknown metal.
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Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on the conservation of mass. In this case, the formula MCl3 indicates that one mole of the metal M combines with three moles of chlorine (Cl). This relationship is crucial for determining the amount of M in the compound based on the moles of Cl provided.
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Empirical and Molecular Formulas

The empirical formula represents the simplest whole-number ratio of elements in a compound, while the molecular formula shows the actual number of atoms of each element. For MCl3, the empirical formula is the same as the molecular formula. Understanding how to derive the molecular formula from the mass and moles of the components is key to finding the atomic mass of the unknown metal M.
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Related Practice
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