Water is often referred to as the universal solvent due to its remarkable ability to dissolve a wide variety of substances, which is essential for many biological processes. In this context, it is important to understand the distinction between a solvent and a solute. The solvent is the substance that performs the dissolving, typically present in larger quantities, while the solute is the substance that is dissolved, usually found in smaller amounts.
For example, when table salt (sodium chloride, NaCl) is added to water, the water acts as the solvent, and the salt is the solute. Sodium chloride consists of sodium cations (Na+) and chloride anions (Cl-) that are held together by ionic bonds. However, when salt is introduced to water, these ionic bonds are disrupted. The water molecules surround the sodium and chloride ions, preventing them from recombining into solid salt. This interaction illustrates how water molecules form a hydration shell around the dissolved ions, facilitating the dissolution process.
The resulting mixture of solute and solvent is known as a solution. Specifically, when water is the solvent, the solution is termed an aqueous solution. The term "aqueous" derives from the Latin word for water, highlighting the role of water in these solutions. Understanding these concepts is crucial as they lay the foundation for exploring how water interacts with various biological molecules, including proteins, nucleic acids, and carbohydrates, in subsequent lessons.