Nonpolar In terms of polarity, water is a molecule. Since lipids are not soluble in water, this same indicates that lipids are classified as polar molecules because substances with different polarities are not soluble in each other.
The Correct Answer and Explanation is:
Correct Answer: polar
Explanation
In terms of polarity, water is a polar molecule. The statement that lipids are not soluble in water is correct, but the conclusion drawn from it is flawed. The fundamental principle governing solubility is “like dissolves like,” which means that polar substances are soluble in other polar substances, and nonpolar substances are soluble in other nonpolar substances. Conversely, polar and nonpolar substances are generally immiscible, meaning they do not mix to form a solution.
The polarity of a water molecule (H₂O) arises from its chemical structure. Oxygen is a highly electronegative atom, meaning it has a strong attraction for electrons. In the covalent bonds between oxygen and the two hydrogen atoms, the electrons are not shared equally. They are pulled closer to the oxygen atom, giving it a slight negative charge (δ-) and leaving the hydrogen atoms with slight positive charges (δ+). This separation of charge, combined with the bent geometry of the molecule, creates a molecular dipole, making water distinctly polar.
Lipids, on the other hand, are composed primarily of long hydrocarbon chains. These chains consist of carbon and hydrogen atoms, which have very similar electronegativity values. As a result, the electrons in the bonds between carbon and hydrogen are shared almost equally, and no significant partial charges develop. This makes the lipid molecule as a whole electrically neutral and nonpolar.
Therefore, when nonpolar lipids are introduced to polar water, they cannot form a solution. The strong cohesive forces between the polar water molecules, known as hydrogen bonds, are much stronger than any potential attraction between the water and the nonpolar lipid molecules. The water molecules effectively exclude the lipid molecules, causing the lipids to clump together. This insolubility of lipids in water is direct evidence that lipids are nonpolar, not polar.
