A solvent is a substance that dissolves other molecules and compounds, known as solutes, to form a solution. While no true “universal solvent” exists that can dissolve every known material, water is frequently referred to by this term. It possesses an exceptional ability to dissolve a vast array of substances, making it unique among common liquids.
Defining the Universal Solvent
A solvent is typically a liquid that dissolves another substance, called a solute, to create a uniform mixture known as a solution. The solvent is usually present in a larger amount within the solution. For instance, when salt dissolves in water, water acts as the solvent and salt is the solute. Water’s designation as a universal solvent highlights its remarkable capacity to dissolve more substances than any other liquid. This includes common materials like table salt, sugar, vinegar, and alcohol.
Water’s Unique Dissolving Power
Water’s exceptional ability to dissolve many substances stems from its unique molecular structure. A water molecule (H₂O) has a bent shape, with an oxygen atom bonded to two hydrogen atoms. The oxygen atom pulls electrons closer to itself, creating a slight negative charge on the oxygen side of the molecule and slight positive charges on the hydrogen sides. This separation of charge makes water a polar molecule, acting like a tiny magnet.
These charged ends allow water molecules to attract each other and interact with other charged or polar molecules. The slightly positive hydrogen ends of one water molecule are attracted to the slightly negative oxygen ends of another, forming what are called hydrogen bonds. This strong network of hydrogen bonds gives water its cohesive properties. When ionic compounds, like salt, or other polar molecules are introduced to water, the water molecules surround and pull apart the solute’s components. This process, known as hydration, effectively dissolves the substance by dispersing its individual ions or molecules throughout the water.
When Water Doesn’t Dissolve
Despite its impressive dissolving capabilities, water does not dissolve everything. Water primarily dissolves polar and ionic substances because of its own polar nature. Conversely, water struggles to dissolve nonpolar substances, such as oils, fats, and waxes. This behavior is explained by the chemical principle “like dissolves like.”
Nonpolar molecules lack the positive and negative regions that water molecules possess, so they are not attracted to water. Instead, water molecules are more attracted to each other through hydrogen bonds than to nonpolar substances. This causes nonpolar substances to remain separate from water, often forming layers or droplets, as seen when oil and water are mixed. This characteristic is relevant in biological systems, such as cell membranes, which are composed of lipid-based molecules that maintain their structure by not dissolving in the watery environment inside and outside cells.