Matter combines in two related forms: mixtures and solutions. Both represent physical combinations of two or more distinct substances. Understanding their similarity requires recognizing that a solution is a specialized version of a mixture. Their common characteristics stem from the fact that no new chemical substances are created when they are formed.
The Foundation: Defining Mixtures
A mixture is the physical combination of two or more substances where each component retains its unique chemical identity. The composition is not fixed; the ratio of components can be varied across a wide range without changing the combination’s fundamental nature. Mixtures are classified based on how uniformly the substances are combined. A heterogeneous mixture is one where the composition is not uniform throughout, such as oil and water. A homogeneous mixture is characterized by having a uniform composition and appearance throughout the sample.
Solutions as a Homogeneous Subset
The core similarity is that a solution is, by definition, a specific type of homogeneous mixture. A solution possesses uniform properties because the components are evenly dispersed at a molecular or ionic level. The particle size is extremely small, ensuring the mixture appears transparent and does not settle out over time. A solution is described by its two main components: the solute and the solvent. The solute is the substance being dissolved, while the solvent is the substance that does the dissolving, usually present in the greatest amount. For example, in saltwater, the salt is the solute and the water is the solvent. Air is a common gaseous solution where nitrogen acts as the solvent.
Shared Characteristics of Physical Combinations
All mixtures, including solutions, are similar because their formation involves only a physical combination, not a chemical reaction. This physical nature ensures that individual substances maintain their original chemical properties, distinguishing them from chemically bonded compounds. For instance, the components of saltwater still exhibit the properties of pure water and pure salt.
Separation Methods
The physical nature of the combination also dictates that the components can be separated by physical means without altering their chemical structure. Simple mixtures can be separated by methods like filtration. Solutions, which are uniform, require techniques that exploit differences in physical properties, such as distillation or evaporation, which leverage the difference in boiling points between the components.
Energy Changes
The process of mixing involves little significant energy change compared to the formation of a chemical compound. While some heat may be absorbed or released when a solution forms, this is due to the breaking and forming of weak intermolecular attractions. In contrast, the formation or breaking of chemical compounds involves substantial energy changes because new chemical bonds are created or destroyed.