Question

For each compound, would you expect greater solubility in water or in hexane? Indicate the kinds of intermolecular forces that would occur between the solute and the solvent in which the molecule is most soluble. a. toluene b. sucrose (table sugar) c. isobutene d. ethylene glycol

Short answer

a. Toluene is more soluble in hexane, with London dispersion forces. b. Sucrose is more soluble in water, with hydrogen bonding. c. Isobutene is more soluble in hexane, with London dispersion forces. d. Ethylene glycol is more soluble in water, with hydrogen bonding.

Step-by-step solution

Analyze Solubility of Toluene

Toluene is a hydrocarbon with a benzene ring and a methyl group. It is nonpolar and has London dispersion forces. Water is a polar solvent and hexane is a nonpolar solvent. Toluene will be more soluble in nonpolar solvents due to similar intermolecular forces (like dissolves like).

Analyze Solubility of Sucrose

Sucrose is a sugar molecule with many hydroxyl (OH) groups capable of forming hydrogen bonds. Water as a polar solvent can form hydrogen bonds, whereas hexane cannot. Therefore, sucrose will be more soluble in water due to the hydrogen bonding.

Analyze Solubility of Isobutene

Isobutene is a nonpolar hydrocarbon with two methyl groups branching off a central carbon chain. It is likely to dissolve better in nonpolar solvents like hexane due to London dispersion forces, similar to toluene.

Analyze Solubility of Ethylene Glycol

Ethylene glycol has two hydroxyl groups capable of forming hydrogen bonds. It is polar and will be more soluble in water due to its ability to form hydrogen bonds with water molecules.

Key concepts

Intermolecular Forces

Understanding intermolecular forces is essential when studying solubility in chemistry. These are the forces that act between molecules to hold them together in a liquid or solid. There are several types of intermolecular forces, with the most common being London dispersion forces, dipole-dipole interactions, and hydrogen bonding.

London dispersion forces are the weakest type of intermolecular force and occur between all molecules, but they are the only type present in nonpolar molecules like isobutene and toluene. This force increases with the size of the molecules or atoms and their ability to polarize.

Dipole-dipole interactions occur between polar molecules that have permanent dipoles. Molecules with different electronegativity values (like water, which is polar) have positive and negative ends, allowing them to be attracted to one another through these interactions.

Finally, hydrogen bonding is a stronger type of dipole-dipole interaction, where a hydrogen atom is bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine. The partially positive hydrogen atom is attracted to a lone pair of electrons on a nearby electronegative atom. Substances like sucrose and ethylene glycol are more soluble in water due to hydrogen bonding.

Polar and Nonpolar Solvents

When dissolving substances, polar and nonpolar solvents play a crucial role. The solubility rule that 'like dissolves like' means that polar solvents tend to dissolve polar substances, while nonpolar solvents dissolve nonpolar substances.

Polar solvents, such as water, have molecules with electrically negative and positive poles. These polar solvents can interact with other polar substances through dipole-dipole interactions or hydrogen bonds, efficiently dissolving them. This explains why substances like sucrose and ethylene glycol, which can form hydrogen bonds, dissolve well in water.

On the other hand, nonpolar solvents like hexane have molecules that do not have significant positive or negative poles. They rely on London dispersion forces for their solubility capabilities, which is why nonpolar molecules, such as toluene and isobutene, are more soluble in them. The ability of a solvent to dissolve a particular solute is essential for many applications, including extraction, purification, and chemical reactions.

Hydrogen Bonding

Among intermolecular forces, hydrogen bonding is particularly significant for solubility in polar solvents like water. It involves a strong attraction between a hydrogen atom attached to an electronegative atom—such as oxygen, nitrogen, or fluorine—and another electronegative atom with a lone pair of electrons.

In the context of solubility, hydrogen bonding greatly enhances the solubility of compounds containing hydroxyl groups (–OH) or similar hydrogen-bonding functional groups in polar solvents. This is observed in the case of sucrose, a molecule with multiple hydroxyl groups that can form numerous hydrogen bonds with water, making it highly soluble. Similarly, ethylene glycol, with its two hydroxyl groups, dissolves effectively in water due to its ability to form hydrogen bonds.

Overall, hydrogen bonds can considerably increase the solubility of a substance in water compared to solvents unable to participate in hydrogen bonding, like nonpolar hexane, which lacks the polar features necessary to create these strong intermolecular attractions.