Which of the following has the lowest melting point? nonane hexane octane decane
The Correct Answer and Explanation is:
Correct Answer: Hexane
Explanation:
The compounds listed — nonane, hexane, octane, and decane — are all part of a group of hydrocarbons called alkanes. Alkanes are saturated hydrocarbons with the general formula CₙH₂ₙ₊₂. These molecules differ in the number of carbon atoms they contain, which directly affects their physical properties such as melting point and boiling point.
Let’s look at the structure of each:
- Hexane: C₆H₁₄
- Octane: C₈H₁₈
- Nonane: C₉H₂₀
- Decane: C₁₀H₂₂
Trend in Melting Points:
In alkanes, melting point increases as the number of carbon atoms in the molecule increases. This trend occurs because larger molecules have more surface area and experience stronger London dispersion forces, which are a type of intermolecular force. These forces must be overcome to change the substance from solid to liquid, so more energy (in the form of heat) is required as the molecule gets larger.
Since hexane has the fewest carbon atoms and the lowest molecular weight among the four, it has the weakest intermolecular forces and therefore the lowest melting point.
Approximate Melting Points for Comparison:
- Hexane: about −95 °C
- Octane: about −57 °C
- Nonane: about −54 °C
- Decane: about −30 °C
As seen from these approximate values, hexane clearly has the lowest melting point among the group.
Conclusion:
Among the given alkanes, hexane has the fewest carbon atoms and weakest intermolecular forces, resulting in the lowest melting point. This demonstrates a consistent trend in physical properties as carbon chain length increases in straight-chain alkanes.
