Which of the following is the general formula for saturated hydrocarbons?
C n H2n + 2
Understanding Saturated Hydrocarbons and Their General Formula
Saturated hydrocarbons are a class of organic compounds that contain only single bonds between carbon atoms. These are also known as alkanes. The term 'saturated' refers to the fact that each carbon atom is bonded to the maximum possible number of hydrogen atoms.
The general formula for saturated hydrocarbons (alkanes) can be derived by looking at the simplest members of this series:
- Methane: \(\text{CH}_4\) (n=1, \(2n+2 = 2(1)+2=4\))
- Ethane: \(\text{C}_2\text{H}_6\) (n=2, \(2n+2 = 2(2)+2=6\))
- Propane: \(\text{C}_3\text{H}_8\) (n=3, \(2n+2 = 2(3)+2=8\))
- Butane: \(\text{C}_4\text{H}_{10}\) (n=4, \(2n+2 = 2(4)+2=10\))
From these examples, we can see a pattern: if there are 'n' carbon atoms, the number of hydrogen atoms is always \(2n + 2\). Therefore, the general formula for saturated hydrocarbons is \(\text{C}_n\text{H}_{2n+2}\).
Analyzing the Options for Saturated Hydrocarbons
Let's examine the given options to determine which one represents the general formula for saturated hydrocarbons:
- Option 1: \(\text{C}_n\text{H}_{2n + 2}\)
This formula matches the pattern observed for alkanes (saturated hydrocarbons). - Option 2: \(\text{C}_n\text{H}_{2n - 2}\)
This is the general formula for alkynes, which are unsaturated hydrocarbons containing a carbon-carbon triple bond. - Option 3: \(\text{C}_n\text{H}_{2n + 1}\)
This formula represents an alkyl group, which is formed by removing one hydrogen atom from an alkane (e.g., methyl \(\text{CH}_3\), ethyl \(\text{C}_2\text{H}_5\)). An alkyl group is not a stable, independent hydrocarbon molecule on its own; it is typically a part of a larger molecule. - Option 4: \(\text{C}_n\text{H}_{2n - 1}\)
This formula can represent various structures depending on the context, but it is not the general formula for saturated hydrocarbons. It might represent certain unsaturated groups. For example, an alkenyl group minus one hydrogen, or related cyclic or branched structures.
Based on the definitions and common formulas in organic chemistry, the general formula for saturated hydrocarbons is \(\text{C}_n\text{H}_{2n + 2}\).
| Type of Hydrocarbon | Bonding | General Formula |
|---|---|---|
| Saturated (Alkanes) | Single bonds only | \(\text{C}_n\text{H}_{2n+2}\) |
| Unsaturated (Alkenes) | At least one double bond | \(\text{C}_n\text{H}_{2n}\) |
| Unsaturated (Alkynes) | At least one triple bond | \(\text{C}_n\text{H}_{2n-2}\) |
Revision Table: Hydrocarbon Formulas
| Formula | Description | Example (n=2) |
|---|---|---|
| \(\text{C}_n\text{H}_{2n+2}\) | Alkanes (Saturated Hydrocarbons) | \(\text{C}_2\text{H}_6\) (Ethane) |
| \(\text{C}_n\text{H}_{2n}\) | Alkenes (Unsaturated) or Cycloalkanes | \(\text{C}_2\text{H}_4\) (Ethene) |
| \(\text{C}_n\text{H}_{2n-2}\) | Alkynes (Unsaturated) or Alkadienes | \(\text{C}_2\text{H}_2\) (Ethyne) |
| \(\text{C}_n\text{H}_{2n+1}\) | Alkyl group | \(\text{C}_2\text{H}_5\) (Ethyl group) |
Additional Information on Hydrocarbons
Hydrocarbons are organic compounds composed entirely of hydrogen and carbon atoms. They are the basic framework for all organic chemistry. Hydrocarbons are broadly classified into aliphatic and aromatic.
- Aliphatic Hydrocarbons: These include alkanes, alkenes, and alkynes, as well as cyclic versions like cycloalkanes. Alkanes are saturated, while alkenes and alkynes are unsaturated due to the presence of double or triple bonds respectively.
- Aromatic Hydrocarbons: These are cyclic compounds with delocalized pi electrons, such as benzene.
Saturated hydrocarbons (alkanes) are generally less reactive than unsaturated hydrocarbons because they only contain relatively strong single bonds. Their reactions often involve the breaking of \(\text{C-H}\) bonds, such as in combustion or halogenation under UV light.
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