mixtures

A mixture is a substance composed of two or more elements or compounds that are physically combined and not chemically bonded. In a mixture, each component keeps its own chemical properties, and the proportions can vary. The components can be separated by physical methods.

Mixtures are classified as homogeneous or heterogeneous. A homogeneous mixture has a uniform composition and appearance throughout, such as air, saltwater, or brass. A heterogeneous mixture has a nonuniform composition, with distinct parts that can often be seen, such as oil and water, granite, or a salad.

Within these categories, common types include solutions, suspensions, and colloids. Solutions are homogeneous mixtures where one substance (the solute) dissolves in another (the solvent), as in salt in water or gas in a liquid. Suspensions are heterogeneous mixtures with particles large enough to settle over time, such as muddy water. Colloids are mixtures with particle sizes between solutions and suspensions; they do not settle and often show the Tyndall effect, as in milk or fog. Emulsions are a subset of colloids involving immiscible liquids held together by emulsifiers, such as mayonnaise.

Separation of mixtures relies on physical properties such as solubility, density, particle size, boiling point, or magnetic properties. Common methods include filtration, decanting, centrifugation, distillation, evaporation, and chromatography. Mixtures contrast with pure substances and with compounds, where chemical bonding produces new substances with distinct properties.