Acetone [(CH3)2CO] is widely used as an industrial solvent. (d) 1-Propanol (CH3CH2CH2OH) has a molecular weight that is very similar to that of acetone, yet acetone boils at 56.5 °C and 1-propanol boils at 97.2 °C. Explain the difference.

Name: Chemistry: The Central Science
Author: Brown
ISBN: 9780134414232

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Identify the molecular structures of acetone and 1-propanol. Acetone is a ketone with the formula (CH3)2CO, while 1-propanol is an alcohol with the formula CH3CH2CH2OH.

Recognize the types of intermolecular forces present in each compound. Acetone primarily exhibits dipole-dipole interactions due to its polar carbonyl group, while 1-propanol exhibits hydrogen bonding due to the presence of the hydroxyl (OH) group.

Understand that hydrogen bonds are generally stronger than dipole-dipole interactions. This means that more energy (in the form of heat) is required to break the hydrogen bonds in 1-propanol compared to the dipole-dipole interactions in acetone.

Relate the strength of intermolecular forces to boiling points. Since 1-propanol has stronger intermolecular forces (hydrogen bonds), it requires a higher temperature to transition from liquid to gas, resulting in a higher boiling point compared to acetone.

Conclude that the difference in boiling points is primarily due to the presence of hydrogen bonding in 1-propanol, which is absent in acetone, leading to stronger intermolecular forces and a higher boiling point for 1-propanol.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Intermolecular Forces

Intermolecular forces are the attractions between molecules that influence physical properties like boiling points. Acetone, being a polar molecule, exhibits dipole-dipole interactions and some hydrogen bonding, while 1-propanol has stronger hydrogen bonding due to its hydroxyl group. The strength and type of these forces significantly affect the energy required to change a substance from liquid to gas.

Molecular Structure and Polarity

The molecular structure and polarity of a compound determine how molecules interact with each other. Acetone has a carbonyl group (C=O) that contributes to its polarity, while 1-propanol has a hydroxyl group (–OH) that enhances its ability to form hydrogen bonds. This difference in structure leads to variations in boiling points, as stronger interactions require more energy to overcome.

Boiling Point and Energy Requirements

The boiling point of a substance is the temperature at which its vapor pressure equals atmospheric pressure, allowing it to transition from liquid to gas. The energy required to reach this point is influenced by the strength of intermolecular forces. In this case, the stronger hydrogen bonding in 1-propanol compared to the weaker interactions in acetone results in a higher boiling point for 1-propanol.

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