Question

Consider water and glycerol, CH \(_{2}(\mathrm{OH}) \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{OH}\) . (a) Would you expect them to be miscible in all proportions? (b) List the intermolecular attractions that occur between a water molecule and a glycerol molecule.

Short answer

(a) Yes, water and glycerol are expected to be miscible in all proportions, as both substances have hydrogen bonds which allow them to easily interact and mix with each other. (b) The intermolecular attractions between a water molecule and a glycerol molecule are primarily hydrogen bonds, resulting from the interaction of the partial positive charges on the hydrogen atoms and the partial negative charges on the oxygen atoms from both substances.

Step-by-step solution

1. Determine the types of intermolecular forces involved

Water has hydrogen bonds, which are a strong type of intermolecular force due to the highly electronegative oxygen atom and the hydrogen atom bonded to it. In glycerol, which is an alcohol (CH\(_{2}\)(OH)CH(OH)CH\(_{2}\)OH), there are also hydrogen bonds, as it has hydroxyl groups (OH) within its structure.

2. Evaluate the miscibility of the two substances based on intermolecular forces

Substances with similar types of intermolecular forces tend to be miscible. Since both water and glycerol have hydrogen bonds, they are likely going to be miscible in all proportions due to the compatibility of their intermolecular forces.

3. Answer part (a) of the exercise

Based on the analysis of the types of intermolecular forces, it is expected that water and glycerol will be miscible in all proportions, as both substances have hydrogen bonds which allow them to easily interact and mix with each other.

4. Identify intermolecular attractions between water and glycerol molecules

The primary intermolecular attractions between water and glycerol molecules are hydrogen bonds. The oxygen atom in the water molecule has a partial negative charge, while the hydrogen atoms have partial positive charges due to the electronegativity difference. In glycerol, the oxygen atoms in the hydroxyl groups (OH) have a partial negative charge and the hydrogen atoms have partial positive charges. These partial charges result in the formation of hydrogen bonds between the water and glycerol.

5. Answer part (b) of the exercise

The intermolecular attractions between a water molecule and a glycerol molecule are primarily hydrogen bonds, resulting from the interaction of the partial positive charges on the hydrogen atoms and the partial negative charges on the oxygen atoms from both substances.

Key concepts

Miscibility

Miscibility refers to the ability of two substances to mix and form a homogeneous solution. In simpler terms, it answers the question of whether two liquids can thoroughly blend with one another. A key factor determining miscibility is the types of intermolecular forces present.
Water and glycerol can serve as an excellent example of miscible substances. Both have strong hydrogen bonds due to their hydroxyl groups (OH) and the highly electronegative nature of oxygen atoms. These bonds enable the molecules to strongly attract and mix with each other. Hence, water and glycerol are miscible in all proportions. This means you can mix them in any ratio, and they will form a consistent and uniform solution.
In general, substances with similar intermolecular forces are more likely to be miscible. For instance, polar molecules mix well with other polar molecules due to their ability to form similar types of bonds. Understanding this principle helps in predicting the miscibility of various chemical combinations.

Hydrogen Bonds

Hydrogen bonds are a type of strong intermolecular force that occur when a hydrogen atom is attracted to a highly electronegative atom, such as oxygen, nitrogen, or fluorine. They are not as strong as covalent or ionic bonds, but they play a significant role in determining the physical properties of molecules, like boiling points and melting points.
In the context of water and glycerol, hydrogen bonds are the primary type of intermolecular attraction. In water, these bonds form because of the interaction between the partial positive charge on hydrogen atoms and the partial negative charge on oxygen atoms.
In glycerol, the story is similar. The hydroxyl groups bring in additional opportunities for hydrogen bonding. The interaction between the hydrogen atoms of one molecule and the oxygen atoms of another creates a network of hydrogen bonds, which makes glycerol an excellent candidate for mixing with water.

• This bonding capability explains why both water and glycerol can easily interact and dissolve in each other.
• Understanding hydrogen bonds helps us grasp how molecules behave in various mixtures.

Additionally, hydrogen bonds are crucial in numerous biological and chemical reactions, further underlining their importance.

Hydroxyl Groups

Hydroxyl groups are functional groups composed of one oxygen atom bonded to one hydrogen atom, represented as OH. These groups are highly polar due to the electronegative nature of the oxygen atom, which draws electrons more strongly than the hydrogen atom.
In the case of glycerol, three hydroxyl groups are present in its molecular structure, contributing to its ability to form hydrogen bonds. The presence of hydroxyl groups makes glycerol comparable to water in terms of intermolecular bonding capabilities.
This polarity makes molecules containing hydroxyl groups, like glycerol, soluble in water. They engage in hydrogen bonding with water molecules, promoting the dissolving process. The more hydroxyl groups a molecule has, generally, the better its solubility in water tends to be.
Hydroxyl groups are highly significant not only because of their role in increasing solubility, but also because:

• They participate in various chemical reactions and influence the physical properties of compounds.
• They are crucial in biological molecules, such as carbohydrates and alcohols.

Therefore, the presence of hydroxyl groups is a key factor not just for miscibility but also for the overall behavior and reactivity of substances.