Hexane is a hydrocarbon (a molecule containing only carbon and hydrogen) with a molecular weight of 86.18 g/mol,
a density of 0.660 g/mL, and a boiling point of 69C.
Pentanol is an alcohol (a hydrocarbon with a "OH" group attached to one of its carbons) with a molecular weight of
88.15 g/mol, a density of 0.814 g/mL, and a boiling point of 137C.
Pentanol has the higher boiling point. Why?
A. The higher molecular weight of pentanol results in a higher boiling point.
B. Hexane has stronger intermolecular forces, so it boils at a lower temperature.
C. Hydrogen bonding requires that a pentanol molecule have more energy to escape the liquid phase.
D. Pentanol is capable of hydrogen bonding, so it goes into the gas phase more easily.
E. The dispersion forces in hexane are weaker.
Look up hydrogen bonding and its effect on boiling point.
the hydrogen bonding
its not D
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Definitely C
To determine why pentanol has a higher boiling point than hexane, we need to consider the molecular structure and intermolecular forces of these compounds.
Firstly, let's analyze the given options:
A. The higher molecular weight of pentanol results in a higher boiling point.
- Molecular weight is a consideration in determining boiling points, but it is not the only factor that determines the boiling point of a substance.
B. Hexane has stronger intermolecular forces, so it boils at a lower temperature.
- This option suggests that hexane has stronger intermolecular forces, but this is not true. Hexane, being a non-polar compound, exhibits weaker intermolecular forces compared to pentanol.
C. Hydrogen bonding requires that a pentanol molecule have more energy to escape the liquid phase.
- Pentanol, being an alcohol, is capable of hydrogen bonding. Hydrogen bonding is a strong intermolecular force that requires more energy to break, resulting in a higher boiling point.
D. Pentanol is capable of hydrogen bonding, so it goes into the gas phase more easily.
- This option is incorrect. Pentanol does have hydrogen bonding, but it makes it harder, not easier, for it to go into the gas phase.
E. The dispersion forces in hexane are weaker.
- This option correctly states that the dispersion forces in hexane are weaker. Dispersion forces (also known as London dispersion forces) are the intermolecular forces between non-polar molecules. These forces arise from temporary shifts in electron density, resulting in temporary dipoles. Hexane, being non-polar, has weaker dispersion forces compared to pentanol, which is polar due to the presence of the hydroxyl group (-OH).
Thus, the correct answer is option E. The dispersion forces in hexane are weaker. Pentanol has higher boiling point due to its ability to form stronger hydrogen bonds, while hexane, being non-polar, exhibits weaker dispersion forces.