The compound XCl4 contains 75.0% Cl by mass. What is the element X?

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Determine the molar mass of Cl (chlorine), which is approximately 35.45 g/mol.

Since the compound XCl4 contains 4 chlorine atoms, calculate the total mass of chlorine in the compound: 4 \times 35.45 \, \text{g/mol}.

Let the molar mass of element X be M. The total molar mass of XCl4 is then M + 4 \times 35.45 \, \text{g/mol}.

Set up the equation for the percentage by mass of Cl in the compound: \frac{4 \times 35.45}{M + 4 \times 35.45} \times 100\% = 75.0\%.

Solve the equation for M to find the molar mass of element X.

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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 case, knowing that XCl4 contains 75.0% Cl by mass allows us to calculate the molar mass of the entire compound and subsequently determine the molar mass of element X.

Stoichiometry

Stoichiometry is the area of chemistry that deals with the relationships between the quantities of reactants and products in chemical reactions. It allows us to use the mass percentages and molar masses to set up equations that can help identify unknown elements in compounds, such as determining the identity of element X in XCl4 based on its mass contribution.

Chemical Formula Interpretation

A chemical formula provides information about the types and numbers of atoms in a compound. In XCl4, the formula indicates that there is one atom of element X and four atoms of chlorine. Understanding how to interpret this formula is crucial for calculating the molar mass and identifying the unknown element based on the given mass percentage of chlorine.

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