Question

Arrange these compounds in order of increasing boiling point (values in \({ }^{\circ} \mathrm{C}\) are \(-42,78\), 138, and 198)

Short answer

Question: Arrange the given compounds in order of increasing boiling points: \(-42{ }^{\circ}\mathrm{C}\), \(78{ }^{\circ}\mathrm{C}\), \(138{ }^{\circ}\mathrm{C}\), and \(198{ }^{\circ}\mathrm{C}\). Answer: The compounds are arranged in order of increasing boiling points as follows: 1. Compound with boiling point \(-42{ }^{\circ}\mathrm{C}\). 2. Compound with boiling point \(78{ }^{\circ}\mathrm{C}\). 3. Compound with boiling point \(138{ }^{\circ}\mathrm{C}\). 4. Compound with boiling point \(198{ }^{\circ}\mathrm{C}\).

Step-by-step solution

Identify the boiling points

We are given four boiling point temperatures: \(-42{ }^{\circ}\mathrm{C}\), \(78{ }^{\circ}\mathrm{C}\), \(138{ }^{\circ}\mathrm{C}\), and \(198{ }^{\circ}\mathrm{C}\).

Arrange the boiling points in increasing order

To arrange these boiling points in increasing order, first find the lowest boiling point, then the next lowest, and so on. Here, the lowest boiling point is \(-42{ }^{\circ}\mathrm{C}\), followed by \(78{ }^{\circ}\mathrm{C}\), then \(138{ }^{\circ}\mathrm{C}\), and finally the highest boiling point is \(198{ }^{\circ}\mathrm{C}\).

Arrangement of compounds

Now that we have arranged the boiling points in increasing order, we can associate each boiling point with its respective compound. The final arrangement of compounds in order of increasing boiling points is: 1. Compound with boiling point \(-42{ }^{\circ}\mathrm{C}\). 2. Compound with boiling point \(78{ }^{\circ}\mathrm{C}\). 3. Compound with boiling point \(138{ }^{\circ}\mathrm{C}\). 4. Compound with boiling point \(198{ }^{\circ}\mathrm{C}\).

Key concepts

Understanding Intermolecular Forces

When it comes to boiling point in organic chemistry, one of the main determining factors is the strength of the intermolecular forces within a compound. Intermolecular forces are the attractive and repulsive forces between molecules. These forces are not as strong as bonds within a molecule (covalent, ionic, etc.), but they are significant enough to influence physical properties like boiling points.

There are several types of intermolecular forces, but the primary ones to consider in organic compounds are van der Waals forces, dipole-dipole interactions, and hydrogen bonding. Van der Waals forces are weak and more prevalent in nonpolar compounds. Dipole-dipole interactions occur when molecules have a permanent dipole moment, with partial positive and negative charges. Hydrogen bonding, a type of dipole-dipole interaction, is particularly strong compared to other intermolecular forces and occurs when hydrogen is bonded to more electronegative atoms such as oxygen, nitrogen, or fluorine.

An understanding of these forces gives us a basis to explain why compound with a boiling point of -42{ }^{}{}{ }^{}C has weaker intermolecular forces compared to the compound that boils at 198{ }^{}{ }^{}C, which has stronger intermolecular forces sustaining its aggregated state to a higher temperature.

Physical Properties of Organic Compounds

The boiling point is one of the several physical properties that can be used to characterize organic compounds, and it provides useful information about the compound's volatility and intermolecular interactions. Physical properties like boiling point, melting point, solubility, and density arise due to the molecular arrangement and chemical nature of these compounds.

It's not just the type of intermolecular force that matters, but also molecular size and shape. As the molecular size (molecular weight) increases, so typically does the boiling point because larger molecules have greater surface area and can experience stronger van der Waals forces. Moreover, branching in molecules can lead to lower boiling points as it decreases the surface area for van der Waals forces to act upon.

In our exercise example, the compounds' boiling points could differ due to a variation in molecular size, the presence or absence of branching, and the strength and type of intermolecular forces. The compound boiling at -42{ }^{}{ }^{}C might be smaller or more branched than the one boiling at 198{ }^{}C.

Arranging Compounds by Boiling Point

Arranging compounds by boiling point provides insight into the comparative strength of their intermolecular forces and can hint at the compounds' structural characteristics. When we have a list of boiling points, like -42{ }^{}{ }^{}C, 78{ }^{}C, 138{ }^{}C, and 198{ }^{}C, we infer that molecules that boil at lower temperatures have weaker intermolecular forces and molecules that boil at higher temperatures have stronger intermolecular forces.

This progressive increase in boiling points helps us to predict the presence of increased molecular weights, stronger intermolecular forces, or less branching in the molecular structure as the boiling points rise. For example, a compound boiling at 198{ }^{}C is likely to be less volatile and have a more complex structure or stronger hydrogen bonding than one boiling at -42{ }^{}C, which is more volatile and likely to have a simpler structure or predominantly van der Waals forces.

In a classroom or homework setting, understanding how to arrange compounds by boiling point can greatly enhance a student's ability to understand chemical properties and predict the behavior of organic compounds under different temperature conditions.