Problem 81 - Chemistry: The Central Science

Question

(a) What is a hydrocarbon? (b) Pentane is the alkane with a chain of five carbon atoms. Write a structural formula for this compound and determine its molecular and empirical formulas.

Step-by-Step Solution

Answer

(a) A hydrocarbon is an organic compound consisting exclusively of hydrogen (H) and carbon (C) atoms, with classes like alkanes, alkenes, alkynes, and aromatic hydrocarbons based on structure and bonding properties. Alkanes are saturated hydrocarbons with single bonds between carbon atoms. (b) Pentane (C_5H_{12}) has the structural formula: H H H H H | | | | | C-C-C-C-C | | | | | H H H H H The molecular formula is C_5H_{12}, and since the greatest common divisor (GCD) of the number of carbon and hydrogen atoms is 1, its empirical formula is also C_5H_{12}.

Step 1: (a) Definition of a Hydrocarbon

A hydrocarbon is an organic compound that consists exclusively of hydrogen (H) and carbon (C) atoms. These compounds can be categorized into various classes such as alkanes, alkenes, alkynes, and aromatic hydrocarbons, based on their structure and bonding properties. Alkanes, specifically, are saturated hydrocarbons with single bonds between carbon atoms.

Step 2: (b) Structural Formula of Pentane

Pentane is an alkane with a chain of five carbon atoms, meaning it has the chemical formula C_5H_{12}. Its structural formula can be represented as: H H H H H | | | | | C-C-C-C-C | | | | | H H H H H

Step 3: (b) Molecular Formula of Pentane

The molecular formula of a compound represents the actual number of atoms of each element present in the molecule. In the case of pentane, the molecular formula is C_5H_{12}, which shows that it consists of 5 carbon atoms and 12 hydrogen atoms.

Step 4: (b) Empirical Formula of Pentane

The empirical formula of a compound represents the simplest whole number ratio of atoms of each element present in the molecule. To determine the empirical formula for pentane, we need to find the greatest common divisor (GCD) of the number of carbon and hydrogen atoms, which is 1 (since 5 is a prime number). Thus, the empirical formula of pentane is the same as its molecular formula, C_5H_{12}.