Understanding the Molecular Formula of Propane

The question asks for the molecular formula of Propane. To answer this, we need to understand what a molecular formula represents and how it relates to the name of an organic compound like propane.

What is a Molecular Formula?

A molecular formula is a way of representing the total number of atoms of each element that are present in a molecule of a substance. For hydrocarbons like propane, it tells us the number of carbon (C) atoms and hydrogen (H) atoms.

Naming Alkanes

Propane is a type of hydrocarbon called an alkane. Alkanes are saturated hydrocarbons, meaning they only contain single bonds between carbon atoms. The names of simple alkanes follow a pattern based on the number of carbon atoms they contain:

• 1 Carbon atom: Methane
• 2 Carbon atoms: Ethane
• 3 Carbon atoms: Propane
• 4 Carbon atoms: Butane
• 5 Carbon atoms: Pentane, and so on.

The suffix "-ane" indicates that it is an alkane.

General Formula for Alkanes

Alkanes follow a general molecular formula which relates the number of carbon atoms (n) to the number of hydrogen atoms. The general formula for an alkane is \(\text{C}_n\text{H}_{2n+2}\), where 'n' is the number of carbon atoms.

Finding the Formula for Propane

From the naming convention, we know that "Propane" refers to an alkane with 3 carbon atoms. So, for propane, the number of carbon atoms, n, is 3. We can use the general formula \(\text{C}_n\text{H}_{2n+2}\) to find its molecular formula:

Substitute n = 3 into the formula:

• Number of Carbon atoms = n = 3
• Number of Hydrogen atoms = \(2n+2 = (2 \times 3) + 2 = 6 + 2 = 8\)

Therefore, the molecular formula for Propane is \(\text{C}_3\text{H}_8\).

Analyzing the Options

Let's look at the given options and compare them with our result:

• Option 1: \(\text{CH}_4\) - This is Methane (n=1: \(2 \times 1 + 2 = 4\))
• Option 2: \(\text{C}_4\text{H}_{10}\) - This is Butane (n=4: \(2 \times 4 + 2 = 10\))
• Option 3: \(\text{C}_3\text{H}_8\) - This is Propane (n=3: \(2 \times 3 + 2 = 8\))
• Option 4: \(\text{C}_2\text{H}_6\) - This is Ethane (n=2: \(2 \times 2 + 2 = 6\))

Comparing our derived formula for Propane (\(\text{C}_3\text{H}_8\)) with the options, we see that Option 3 matches.

Summary Table of First Few Alkanes

Based on the general formula and the analysis of the options, the molecular formula for Propane is indeed \(\text{C}_3\text{H}_8\).

Revision Table: Alkane Formulas

Additional Information: Hydrocarbons and Formulas

Hydrocarbons are organic compounds made up entirely of hydrogen and carbon atoms. They are classified based on the types of bonds between the carbon atoms:

• Alkanes: Contain only single bonds (saturated). General formula: \(\text{C}_n\text{H}_{2n+2}\). Examples: Methane, Ethane, Propane.
• Alkenes: Contain at least one carbon-carbon double bond (unsaturated). General formula: \(\text{C}_n\text{H}_{2n}\) (for non-cyclic alkenes). Examples: Ethene (\(\text{C}_2\text{H}_4\)), Propene (\(\text{C}_3\text{H}_6\)).
• Alkynes: Contain at least one carbon-carbon triple bond (unsaturated). General formula: \(\text{C}_n\text{H}_{2n-2}\) (for non-cyclic alkynes). Examples: Ethyne (\(\text{C}_2\text{H}_2\)), Propyne (\(\text{C}_3\text{H}_4\)).

Understanding these general formulas helps in determining the molecular formula of many simple hydrocarbons given their name or structure.