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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 104a
Chapter 3, Problem 104a

From the given molar mass and empirical formula of several compounds, find the molecular formula of each compound. a. C4H9, 114.22 g/mol

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1
Determine the molar mass of the empirical formula C_4H_9 by calculating the sum of the atomic masses of its constituent atoms.
Calculate the molar mass of the empirical formula: (4 \(\times\) \(\text{atomic mass of C}\)) + (9 \(\times\) \(\text{atomic mass of H}\)).
Divide the given molar mass of the compound (114.22 g/mol) by the molar mass of the empirical formula to find the ratio (n) between the molecular and empirical formulas.
Multiply the subscripts in the empirical formula C_4H_9 by the ratio (n) to obtain the molecular formula.
Write the molecular formula using the new subscripts obtained from the multiplication.

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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. It provides essential information about the composition of the compound but does not indicate the actual number of atoms present. For example, the empirical formula for glucose (C6H12O6) is CH2O, which shows the ratio of carbon, hydrogen, and oxygen atoms.
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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. In the context of the question, knowing the molar mass allows us to determine how many times the empirical formula fits into the molecular formula, which is crucial for finding the correct molecular formula.
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Molecular Formula

The molecular formula indicates the actual number of each type of atom in a molecule of a compound. It can be derived from the empirical formula by multiplying the subscripts by a whole number, which is determined by the ratio of the compound's molar mass to the empirical formula mass. For instance, if the empirical formula is C4H9 and the molar mass is 114.22 g/mol, we can find the molecular formula by comparing the empirical formula mass to the given molar mass.
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