Textbook Question
The compound XCl4 contains 75.0% Cl by mass. What is the element X?
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Ch.3 - Chemical Reactions and Reaction Stoichiometry
Chapter 3, Problem 52b
What is the molecular formula of each of the following compounds? (b) empirical formula C2H4O, molar mass = 88.0 g/mol
Verified step by step guidance1
1. First, calculate the molar mass of the empirical formula, C<sub>2</sub>H<sub>4</sub>O. The molar mass of carbon (C) is approximately 12.01 g/mol, hydrogen (H) is approximately 1.01 g/mol, and oxygen (O) is approximately 16.00 g/mol. Multiply each of these by the number of each atom in the empirical formula and add them together.
2. Once you have the molar mass of the empirical formula, divide the given molar mass of the compound (88.0 g/mol) by the molar mass of the empirical formula. This will give you a ratio.
3. Round this ratio to the nearest whole number. This number represents the number of empirical formula units per molecule of the compound.
4. Multiply the subscripts in the empirical formula by this ratio to get the molecular formula. This is the actual number of atoms of each element in a molecule of the compound.
5. The result is the molecular formula of the compound.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Empirical Formula
The empirical formula represents the simplest whole-number ratio of atoms in a compound. For example, the empirical formula C2H4O indicates that for every two carbon atoms, there are four hydrogen atoms and one oxygen atom. It does not provide information about the actual number of atoms in a molecule, which can be determined by the molecular formula.
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Empirical vs Molecular Formula
Molecular Formula
The molecular formula gives the actual number of each type of atom in a molecule of a compound. It is derived from the empirical formula by multiplying the subscripts by a whole number, known as the molecular weight factor. In this case, the molecular formula can be determined by comparing the molar mass of the compound to the molar mass of the empirical formula.
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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 molecular formula. For the compound with an empirical formula of C2H4O and a molar mass of 88.0 g/mol, this value is crucial for determining the molecular formula by comparing it to the molar mass of the empirical formula.
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Related Practice
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Determine the empirical and molecular formulas of each of the following substances: (b) Caffeine, a stimulant found in coffee, contains 49.5% C, 5.15% H, 28.9% N, and 16.5% O by mass and has a molar mass of 195 g/mol.
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