Hexane is a hydrocarbon with the chemical formula C6H14. It is a nonpolar molecule, meaning it has a relatively equal distribution of electrons and lacks any significant positive or negative charges. On the other hand, water (H2O) is a polar molecule, with oxygen having a partial negative charge and hydrogen having a partial positive charge. This polarity arises due to the difference in electronegativity between oxygen and hydrogen atoms.
When hexane is added to water, the polar water molecules are more attracted to each other than they are to the nonpolar hexane molecules. This is because water molecules can form hydrogen bonds with each other, which are strong intermolecular forces. These hydrogen bonds occur due to the attraction between the partially positive hydrogen atom of one water molecule and the partially negative oxygen atom of another water molecule.
In contrast, hexane does not have any polar groups or hydrogen atoms bonded to highly electronegative atoms like oxygen or nitrogen. As a result, it cannot form hydrogen bonds with water molecules. Instead, hexane molecules are held together by weaker dispersion forces, also known as London forces or Van der Waals forces. These forces arise due to temporary fluctuations in electron distribution that create temporary dipoles in molecules. While dispersion forces are present in all molecules to some extent, they are generally weaker than hydrogen bonds.
The difference in intermolecular forces between water and hexane leads to their inability to mix readily. The water molecules prefer to interact with each other through hydrogen bonding, while the hexane molecules are attracted to one another through dispersion forces. This preference for like molecules is known as “like dissolves like.” Since hexane and water have different intermolecular forces, they do not mix well, resulting in the insolubility of hexane in water.
To further illustrate this, consider the example of oil and water. Just like hexane, oil consists of nonpolar molecules and is insoluble in water. When oil is added to water, it forms distinct separate layers. This separation occurs because the water molecules form hydrogen bonds with each other, while the nonpolar oil molecules are excluded from this network and instead aggregate with other oil molecules.
The insolubility of hexane in water can be attributed to the differences in intermolecular forces. The polar nature of water and its ability to form hydrogen bonds lead to strong attractions between water molecules, making them less likely to interact with nonpolar hexane molecules. Instead, hexane molecules prefer to interact with each other through weaker dispersion forces, resulting in the immiscibility of hexane and water.