Question

The boiling points of water, ethanol and diethyl ether are \(100^{\circ} \mathrm{C}\) and \(78.5^{\circ} \mathrm{C}\) and \(34.6^{\circ} \mathrm{C}\) respectively. The intermolecular forces will be in the order: (a) water \(>\) ethanol \(>\) diethyl ether (b) ethanol \(>\) water \(>\) diethyl ether (c) diethyl ether \(>\) ethanol \(>\) water

Short answer

The intermolecular forces will be in the order of water \(>\) ethanol \(>\) diethyl ether.

Step-by-step solution

Understand the problem

Identify that the problem is asking for the order of intermolecular forces in the given substances based on their boiling points. Understand the relationship between boiling point and intermolecular forces - substances with higher boiling points have stronger intermolecular forces.

Order substances based on boiling points

List water, ethanol, and diethyl ether in order of their boiling points, where the substance with highest boiling point is first and the one with the lowest boiling point is last. In this case, the order is: water \(100^{\circ} \mathrm{C}\), ethanol \(78.5^{\circ} \mathrm{C}\) and diethyl ether \(34.6^{\circ} \mathrm{C}\).

Order substances correspondingly in terms of intermolecular forces

Knowing the relationship between boiling point and intermolecular forces, order the substances in the same order in terms of intermolecular forces. Therefore, the intermolecular forces will be in the order: water \(>\) ethanol \(>\) diethyl ether.

Key concepts

Boiling Point Relationship

The boiling point of a substance is a critical physical property that is directly related to the strength of its intermolecular forces. Intermolecular forces are the attractions between molecules, which hold them together in a liquid state. These forces must be overcome to transition the substance from liquid to gas during boiling.

Substances with strong intermolecular forces require more energy to separate the molecules; hence, they have higher boiling points. It follows that if we know the boiling points of several substances, we can predict the relative strength of their intermolecular attractions. For example, water has a higher boiling point than ethanol, which, in turn, has a higher boiling point than diethyl ether. This indicates that water has the strongest intermolecular forces, followed by ethanol, then diethyl ether. Therefore, the correct order of intermolecular strength based on boiling points is: water > ethanol > diethyl ether.

This relationship is central to many applications in chemistry, including distillation and purification methods, where boiling points are used to separate substances with different intermolecular strength.

Physical Chemistry Education

Grasping the concepts of intermolecular forces and their implications on properties like boiling point is a fundamental aspect of physical chemistry education. As we have seen, understanding these concepts helps in predicting physical properties of substances, which is crucial for many experiments and industrial processes.

In an academic setting, learners are introduced to the theory followed by practical examples. This step-by-step approach, as illustrated in the textbook exercise, ensures that students build a strong foundation. It is important for educators to explain not only the 'how' but also the 'why' behind the chemical phenomena, as this promotes deeper understanding. For instance, rather than simply memorizing that water has a higher boiling point than ethanol and diethyl ether, students should understand that this is due to hydrogen bonding, which is a particularly strong type of intermolecular force present in water molecules.

Engaging students in discussions, laboratory experiments and problem-solving exercises helps to cement these concepts and their applications in real-world scenarios.

Intermolecular Interactions Comparison

Intermolecular interactions such as hydrogen bonds, London dispersion forces, and dipole-dipole interactions exist to varying degrees in different substances and affect their boiling points. As previously discussed, water forms strong hydrogen bonds because it has highly polar O-H bonds, leading to a higher boiling point.

Ethanol, though it can also form hydrogen bonds, has a larger alkyl group compared to water which increases its surface area and induces weaker London dispersion forces. As a result, even though ethanol can form hydrogen bonds, its overall intermolecular interactions are not as strong as those in water. Diethyl ether, on the other hand, cannot form hydrogen bonds as effectively due to its ether linkage and has two large alkyl groups, resulting in its intermolecular forces being primarily based on even weaker London dispersion forces.

Understanding the different intermolecular interactions can explain why substances with similar molecular weights might have dramatically different boiling points. Educators need to emphasize these comparisons amongst different types of intermolecular interactions to provide students with a comprehensive understanding of how such forces dictate the physical properties of substances.