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Ch.2 - Atoms, Molecules, and Ions
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.2 - Atoms, Molecules, and IonsProblem 81b2
Chapter 2, Problem 81b2

(b) Pentane is the alkane with a chain of five carbon atoms. Determine its molecular formula.

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1
Identify the general formula for alkanes, which is C_nH_{2n+2}.
Recognize that pentane has a chain of five carbon atoms, so n = 5.
Substitute n = 5 into the general formula: C_5H_{2(5)+2}.
Calculate the number of hydrogen atoms: 2(5) + 2 = 12.
Write the molecular formula for pentane as C_5H_{12}.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Alkanes

Alkanes are a class of hydrocarbons characterized by single bonds between carbon atoms. They follow the general formula CnH2n+2, where 'n' represents the number of carbon atoms. This structure results in saturated compounds, meaning they contain the maximum number of hydrogen atoms possible for a given number of carbon atoms.
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Molecular Formula

The molecular formula of a compound indicates the number and types of atoms present in a molecule. For alkanes, the molecular formula can be derived from the number of carbon atoms in the chain. For pentane, which has five carbon atoms, the molecular formula can be calculated using the formula CnH2n+2.
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Carbon Chain Length

The length of the carbon chain in alkanes directly influences their molecular formula and properties. In the case of pentane, the chain consists of five carbon atoms, which determines the specific arrangement and number of hydrogen atoms. Understanding the relationship between chain length and molecular formula is essential for identifying and naming alkanes.
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Related Practice
Textbook Question

Write the chemical formula for each substance mentioned in the following word descriptions (use the front inside cover to find the symbols for the elements you do not know). (b) On treatment with hydrofluoric acid, silicon dioxide forms silicon tetrafluoride and water. (use the front inside cover to find the symbols for the elements you do not know). (c) Sulfur dioxide reacts with water to form sulfurous acid. (use the front inside cover to find the symbols for the elements you do not know). (d) The substance phosphorus trihydride, commonly called phosphine, is a toxic gas. (e) Perchloric acid reacts with cadmium to form cadmium(II) perchlorate.

Textbook Question

Assume that you encounter the following sentences in your reading. What is the chemical formula for each substance mentioned? (c) Hydrogen cyanide is a very poisonous gas.

Textbook Question

(a) What is a hydrocarbon?

Textbook Question

(b) Pentane is the alkane with a chain of five carbon atoms. Determine its empirical formula.

Textbook Question

(a) What is meant by the term isomer?

Textbook Question

(b) Among the four alkanes, ethane, propane, butane, and pentane, which is capable of existing in isomeric forms?