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Ch.3 - Molecules and Compounds
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Not the one you use?Change textbook
All textbooksTro 6th EditionCh.3 - Molecules and CompoundsProblem 126
Chapter 3, Problem 126

A metal (M) forms an oxide with the formula M2O. If the oxide contains 16.99% O by mass, what is the identity of the metal?

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Calculate the molar mass of oxygen (O), which is approximately 16.00 g/mol.
Let the molar mass of the metal (M) be represented as x g/mol.
The molar mass of the oxide M2O is 2x + 16.00 g/mol.
Set up the equation for the mass percentage of oxygen: (16.00 / (2x + 16.00)) * 100 = 16.99.
Solve the equation for x to find the molar mass of the metal M.

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Key Concepts

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

Molar Mass and Percent Composition

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole. Percent composition refers to the percentage by mass of each element in a compound. In this question, knowing the percent composition of oxygen in the oxide allows us to calculate the molar mass of the metal by using the formula for percent composition.
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Stoichiometry

Stoichiometry is the branch of chemistry that deals with the relationships between the quantities of reactants and products in chemical reactions. In this case, the stoichiometric ratio of the metal (M) to oxygen in the oxide M2O is crucial for determining the molar mass of the metal based on the given mass percentage of oxygen.
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Identifying Elements from Molar Mass

Once the molar mass of the metal is calculated, it can be compared to known molar masses of elements on the periodic table to identify the metal. Each element has a unique molar mass, and this comparison allows us to determine which metal corresponds to the calculated value based on the oxide's formula.
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Related Practice
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Textbook Question

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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