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In chemistry, a mixture consists of two or more distinct substances that are physically combined but retain their individual chemical identities. The components do not form new chemical bonds; instead, they coexist, allowing each to maintain its own properties.
Three key criteria define a mixture:
A homogeneous mixture has a uniform composition throughout. Any sample taken from the mixture contains the same proportion of constituents. Classic example: salt dissolved in water, forming a clear, uniform solution.
In contrast, a heterogeneous mixture contains visibly distinct regions or phases. The composition varies from one part to another. Think of a bowl of cereal or a chocolate‑chip cookie, where different components are easily discernible.
Mixtures can also be categorized by the size of their dispersed particles:
Solutions feature particles smaller than 1 nm, so they cannot be separated by centrifugation or decantation. Air—composed of gases—serves as a familiar example.
Colloids contain particles between 1 nm and 1 µm. Although they appear uniform to the naked eye, a microscope reveals their uneven distribution. Centrifugation can separate them. Hair spray, a liquid aerosol dispersed in gas, exemplifies a colloid.
Suspensions have larger particles that may settle over time. Stabilizing agents are often added to prevent rapid separation. Both decantation and centrifugation can retrieve the dispersed phase. Salad dressing, where oil droplets rest atop vinegar, illustrates a suspension.
