The structural formulas of the compounds n-butane and isobutane are shown below. (b) Determine the empirical formula of each.
Ch.2 - Atoms, Molecules, and Ions
Chapter 2, Problem 47a
What are the molecular and empirical formulas for each of the following compounds? Write the molecular formula for the following compound.


1
Identify the molecular formula for dodecane by counting the number of carbon (C) and hydrogen (H) atoms in the structure.
For dodecane, count the carbon atoms: there are 12 carbon atoms.
Count the hydrogen atoms in dodecane: there are 26 hydrogen atoms.
Write the molecular formula for dodecane: C12H26.
For methane, count the carbon and hydrogen atoms: there is 1 carbon atom and 4 hydrogen atoms. Write the molecular formula for methane: CH4.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Molecular Formula
The molecular formula of a compound indicates the actual number of each type of atom present in a molecule. For example, dodecane has the molecular formula C12H26, which shows it contains 12 carbon atoms and 26 hydrogen atoms. This formula provides insight into the composition of the molecule but does not convey structural information.
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Empirical Formula
The empirical formula represents the simplest whole-number ratio of the elements in a compound. For dodecane (C12H26), the empirical formula is C6H13, indicating that the ratio of carbon to hydrogen is 6:13. This formula is useful for understanding the basic composition of a compound without detailing the actual number of atoms.
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Structural Formula
A structural formula provides a visual representation of the arrangement of atoms within a molecule, showing how atoms are bonded together. In the case of dodecane and methane, the structural formulas illustrate the linear chain of carbon atoms in dodecane and the tetrahedral arrangement of hydrogen atoms around a single carbon atom in methane. This information is crucial for understanding the chemical behavior and properties of the compounds.
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Related Practice
Textbook Question
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Textbook Question
The structural formulas of the compounds n-butane and isobutane are shown below. (c) Which formulas—empirical, molecular, or structural—allow you determine these are different compounds?
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Ball-and-stick representations of benzene, a colorless liquid often used in organic chemistry reactions, and acetylene, a gas used as a fuel for high-temperature welding, are shown below. (a) Determine the molecular formula of each.
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Two substances have the same molecular and empirical formulas. Does this mean that they must be the same compound?
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Write the empirical formula corresponding to each of the following molecular formulas: (a) Al2Br6
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Textbook Question
Write the empirical formula corresponding to each of the following molecular formulas: (b) C8H10
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