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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 140
Chapter 3, Problem 140

A phosphorus compound that contains 34.00% phosphorus by mass has the formula X3P2. Identify the element X.

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Start by determining the molar mass of phosphorus (P), which is approximately 30.97 g/mol.
Assume you have 100 g of the compound, which means you have 34.00 g of phosphorus.
Calculate the moles of phosphorus in the compound using the formula: \( \text{moles of P} = \frac{\text{mass of P}}{\text{molar mass of P}} \).
Since the formula is X3P2, there are 2 moles of phosphorus for every 3 moles of element X. Use the moles of phosphorus to find the moles of X.
Calculate the molar mass of element X using the formula: \( \text{molar mass of X} = \frac{\text{mass of X}}{\text{moles of X}} \), where the mass of X is the remaining mass after accounting for phosphorus.

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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. To identify the element X in the compound X3P2, we can use the given percent composition of phosphorus to calculate the total molar mass of the compound and subsequently determine the molar mass of element X.
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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 in a molecule. In this case, X3P2 is the molecular formula, and understanding how to derive the empirical formula can help in identifying the element X by comparing the ratios of phosphorus to X.
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Atomic Mass and Element Identification

Each element has a unique atomic mass, which is the weighted average mass of its isotopes. By calculating the molar mass of the compound X3P2 using the known mass percentage of phosphorus and the molar mass of phosphorus, we can find the molar mass of X. This value can then be compared to known atomic masses of elements to identify X.
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Related Practice
Textbook Question

Write the structural formulas of three different compounds that each have the molecular formula C5H12.

Textbook Question

Phosphorus is obtained primarily from ores containing calcium phosphate. If a particular ore contains 57.8% calcium phosphate, what minimum mass of the ore must be processed to obtain 1.00 kg of phosphorus?

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Textbook Question

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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Textbook Question

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Textbook Question

Element A is an atomic element, and element B is a diatomic molecular element. Using circles to represent atoms of A and squares to represent atoms of B, draw molecular-level views of each element.