Question

Glycerol has a higher surface tension than water. What can you say about the relative strength of the intermolecular forces in the two compounds? Which has a higher boiling point?

Short answer

Glycerol has stronger intermolecular forces and a higher boiling point than water.

Step-by-step solution

- Understand Surface Tension

Surface tension is a measure of the cohesive forces acting at the surface of a liquid. The stronger the intermolecular forces within the liquid, the higher the surface tension.

- Compare Surface Tensions

Since glycerol has a higher surface tension than water, this indicates that the intermolecular forces in glycerol are stronger than those in water.

- Understand Boiling Point

Boiling point is another property that depends on the strength of intermolecular forces. A higher boiling point indicates stronger intermolecular forces because more energy is required to break these forces during the phase change from liquid to gas.

- Compare Boiling Points

Given that glycerol has stronger intermolecular forces than water, it follows that glycerol will also have a higher boiling point.

Key concepts

surface tension

Surface tension is a fascinating property of liquids that makes the surface behave like a stretched elastic membrane. This phenomenon is due to the cohesive forces between molecules at the surface of the liquid. These cohesive forces pull the molecules inward, creating pressure that minimizes the surface area. The stronger the intermolecular forces, the higher the surface tension.
In comparing glycerol and water, glycerol demonstrates higher surface tension. This means the cohesive forces among glycerol molecules are stronger than those among water molecules. Why? Because in glycerol, the hydrogen bonding is more prominent due to three hydroxyl (OH) groups compared to water’s single OH group per molecule.
Understanding surface tension helps us comprehend many everyday phenomena, like why some insects can walk on water or why small droplets form on surfaces instead of spreading out.

boiling point

The boiling point of a liquid is the temperature at which it changes from a liquid to a gas. This phase change happens when the molecules have enough energy to break free from intermolecular forces holding them as a liquid. Consequently, the strength of these intermolecular forces directly impacts the boiling point.
For instance, glycerol has stronger intermolecular forces compared to water, primarily due to its ability to form more hydrogen bonds. This superior strength in bonding means more energy is needed to separate the glycerol molecules during boiling. Thus, glycerol has a higher boiling point than water.
Understanding boiling points isn’t just theoretical. It has practical applications in cooking, distillation processes, and understanding natural phenomena like why some substances evaporate faster than others.

glycerol vs water

Glycerol and water, while both being common liquids, contrast significantly due to their molecular structures and properties.
Glycerol, also known as glycerin, has three hydroxyl (OH) groups, making it highly capable of forming strong hydrogen bonds. These multiple hydrogen bonds contribute to glycerol’s higher viscosity, higher surface tension, and higher boiling point compared to water.
Water, with its two hydrogen atoms and one oxygen atom (H₂O), can also form hydrogen bonds, but it only has one OH group per molecule. This makes its intermolecular forces weaker compared to glycerol. Hence, water has a lower surface tension and lower boiling point.
These differences are crucial in various applications. For example, glycerol's properties make it ideal for use in skincare products as a moisturizer, while water’s properties make it a universal solvent, vital to all biological systems.
In summary, understanding the differences in surface tension, boiling point, and molecular structure between glycerol and water provides insight into their unique behaviors and practical uses.