Which formula represents a saturated hydrocarbon?
(a) C4H8
(b) C5H12
(c) C4H6
(d) C5H10
Ans: (b) C5H12
Understanding Saturated Hydrocarbons
Saturated hydrocarbons, also known as alkanes, are characterized by having only single bonds between their carbon atoms. This means that each carbon atom is bonded to the maximum possible number of hydrogen atoms.
- General Formula: Alkanes follow the general formula CₙH₂n+₂, where ‘n’ is the number of carbon atoms.
Let’s examine why the other options are incorrect:
- (a) C₄H₈: This formula fits the general formula for alkenes (CₙH₂<0xE2><0x82><0x99>), which contain at least one carbon-carbon double bond, making them unsaturated.
- (c) C₄H₆: This formula suggests the presence of multiple double or triple bonds, indicating an unsaturated hydrocarbon.
- (d) C₅H₁₀: Similar to (a), this formula corresponds to an alkene, an unsaturated hydrocarbon.
Why C₅H₁₂ is Saturated
Using the general formula for alkanes (CₙH₂<0xE2><0x82><0x99><0xE2><0x82><0x8B>₂), if n=5:
- H = (2 * 5) + 2 = 12
Therefore, C₅H₁₂ perfectly fits the alkane formula, representing a saturated hydrocarbon (pentane).
Key Differences: Saturated vs. Unsaturated
- Saturated (Alkanes):
- Contain only single carbon-carbon bonds.
- Follow the general formula CₙH₂<0xE2><0x82><0x99><0xE2><0x82><0x8B>₂.
- Relatively unreactive.
- Examples: methane (CH₄), ethane (C₂H₆), propane (C₃H₈).
- Unsaturated (Alkenes and Alkynes):
- Contain at least one carbon-carbon double (alkenes) or triple (alkynes) bond.
- Alkenes follow the general formula CₙH₂<0xE2><0x82><0x99>.
- Alkynes follow the general formula CₙH₂<0xE2><0x82><0x99>−₂
- More reactive due to the presence of multiple bonds.
- Examples: ethene (C₂H₄), propene (C₃H₆), ethyne (C₂H₂).
Significance
The distinction between saturated and unsaturated hydrocarbons is crucial in understanding their properties and applications:
- Saturated hydrocarbons are commonly used as fuels due to their efficient combustion.
- Unsaturated hydrocarbons are essential building blocks for polymers and other synthetic materials.
Understanding these fundamental concepts in organic chemistry allows us to better comprehend the diverse world of carbon-based compounds and their impact on our daily lives.
