Which compounds can dissolve in water?

Understanding What Dissolves in Water

Water is often called the universal solvent, but it does not dissolve everything equally well. Whether a substance mixes seamlessly with water comes down to its fundamental chemical structure. In chemistry, the golden rule is that "like dissolves like," meaning that water—a highly polar molecule—interacts best with other polar or charged materials.

Because of this principle, ionic compounds like table salt dissolve easily in water. The positive and negative ions in these compounds are readily pulled apart and surrounded by water's charged ends. Similarly, polar molecular compounds, such as table sugar or simple alcohols, dissolve well because they can form strong hydrogen bonds with water molecules.

In contrast, aliphatic and aromatic compounds—which make up most fats, oils, and hydrocarbons—are predominantly nonpolar. Lacking electrical charges, they cannot interact effectively with water molecules, making them naturally insoluble and causing them to separate into distinct layers.

However, nonpolar molecules are not entirely stuck that way. Adding polar functional groups (such as hydroxyl or carboxyl groups) to an aliphatic or aromatic structure significantly boosts its ability to mix with water. This clever structural modification is widely used in pharmaceutical design to ensure that medications can dissolve and travel effectively through the human body.