Why is heptane more soluble in octane than in water? What intermolecular forces are responsible for this?
The Correct Answer and Explanation is:
Heptane is more soluble in octane than in water due to the similar nature of their molecular structures, particularly the intermolecular forces at play. Both heptane and octane are nonpolar hydrocarbons, composed of long carbon chains with hydrophobic (water-repelling) characteristics. Because of this similarity, they experience comparable types of intermolecular interactions, specifically London dispersion forces, which are the weakest type of van der Waals forces.
In contrast, water is a highly polar molecule with hydrogen bonding capability. Water molecules interact strongly with each other via hydrogen bonds, creating a tightly bound network that favors solubility for other polar substances or those that can hydrogen bond (e.g., salts or alcohols). Since heptane is nonpolar and does not engage in hydrogen bonding, it does not mix well with water. When mixed with water, the water molecules preferentially interact with each other rather than with heptane molecules, leading to phase separation.
On the other hand, heptane and octane, both nonpolar, interact primarily through London dispersion forces. These forces arise from temporary fluctuations in electron density, creating transient dipoles that attract neighboring molecules. Because the molecular structure and polarity of heptane and octane are so similar, they can dissolve in each other more readily than in water.
In summary, the solubility of heptane in octane is largely driven by the similarity in their nonpolar nature and the ability of London dispersion forces to operate between them. In contrast, the polarity and hydrogen bonding in water prevent it from dissolving nonpolar substances like heptane effectively.
