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. Hydrogen bonding requires that a pentanol molecule have more energy to escape the liquid phase.
B. Pentanol is capable of hydrogen bonding, so it goes into the gas phase more easily.
C. Hexane has stronger intermolecular forces, so it boils at a lower temperature.
D. The higher molecular weight of pentanol results in a higher boiling point.
E. The dispersion forces in hexane are weaker.
----i've seen that others have posted this question and after thinking about it i thinks its c. im i right?
D --> London's dispersion force.
Both missed it. The answer is A.
B. Pentanol IS capable of hydrogen bonding (so far so good) so it makes the boiling point higher, not lower.
C. Hexane has WEAKER intermolecular forces (or said another way, pentanol, because it's an alcohol, has stronger intermolecular forces;; again, hydrogen bonding----
D. Generally it is true that higher molecular weights result in higher boiling points but we are talking about only two units here and that isn't enough to make much difference.
E. The dispersion forces in the two are more or less the same, especially, since the molar mass is about the same.
DrBob222....you are INCORRECT!!!! Lord, this is not the first time you have been wrong....just stop answering questions that you have no idea about, fake doctor.......
Lol Dr. Bob must not be a Doctor lol.
To determine the correct answer, we need to analyze the properties and intermolecular forces of both hexane and pentanol.
Hexane is a nonpolar molecule consisting of only carbon and hydrogen atoms. It experiences London dispersion forces, which are weak intermolecular forces caused by temporary fluctuations in electron density. Dispersion forces are generally weaker in smaller, more compact molecules.
Pentanol, on the other hand, is an alcohol molecule. It contains a hydroxyl group (OH) attached to one of its carbons, which makes it a polar molecule. The oxygen atom in the hydroxyl group has a partial negative charge, and the hydrogen atom has a partial positive charge. This polarity leads to hydrogen bonding, which is a much stronger intermolecular force compared to dispersion forces.
Now, let's consider the options:
A. Hydrogen bonding requires that a pentanol molecule have more energy to escape the liquid phase.
This statement is incorrect. Hydrogen bonding does require more energy to break the intermolecular interactions, but it is not directly related to boiling point.
B. Pentanol is capable of hydrogen bonding, so it goes into the gas phase more easily.
This statement is incorrect. Hydrogen bonding doesn't make a substance go into the gas phase more easily. The boiling point is the temperature at which a substance changes from a liquid to a gas.
C. Hexane has stronger intermolecular forces, so it boils at a lower temperature.
This statement is incorrect. Hexane experiences weaker dispersion forces compared to pentanol's hydrogen bonding. Hexane has a lower boiling point due to its weaker intermolecular forces.
D. The higher molecular weight of pentanol results in a higher boiling point.
This statement is partially correct. Generally, molecules with higher molecular weights tend to have higher boiling points. However, the molecular weights of hexane and pentanol are relatively close, so it's not the primary reason for the difference in boiling points.
E. The dispersion forces in hexane are weaker.
This statement is correct. Hexane experiences only dispersion forces, which are generally weaker than hydrogen bonding. Therefore, pentanol has a higher boiling point due to the stronger intermolecular forces provided by hydrogen bonding.
In conclusion, the correct answer is B. Pentanol's higher boiling point is primarily due to its capability of forming hydrogen bonds, which are stronger intermolecular forces compared to the dispersion forces experienced by hexane.