Dispersion
Definition and meaning of Dispersion in chemistry.
Dispersion is a mixture in which particles of one substance, called the dispersed phase, are distributed throughout a continuous substance called the dispersion medium, without the dispersed particles necessarily dissolving to form a true solution.
In more detail
Dispersions are classified by the size of the dispersed particles: true solutions contain individual ions or molecules smaller than about 1 nanometer, colloids contain particles roughly 1 to 1000 nanometers, and coarse suspensions contain still larger particles that eventually settle under gravity. Colloidal dispersions are stable indefinitely because thermal motion keeps the particles suspended, and they scatter visible light through the Tyndall effect, which distinguishes them from true solutions. The dispersed phase and dispersion medium can each be a solid, liquid, or gas, giving rise to familiar systems such as aerosols, foams, gels, and emulsions.
Key facts
| Field | General Chemistry |
|---|---|
| Colloidal particle size | ~1–1000 nm |
| Diagnostic test | Tyndall effect (light scattering) |
| Related mixture types | solution, colloid, suspension |
Milk is a colloidal dispersion (specifically an emulsion) in which microscopic fat droplets, the dispersed phase, are distributed throughout water, the dispersion medium.
Frequently asked questions
How is a dispersion different from a true solution?
In a true solution the solute is broken down to individual ions or molecules (under about 1 nm) and is uniformly mixed at the molecular level, while in a dispersion the dispersed particles are larger aggregates that remain a physically distinct phase, even though colloidal dispersions do not separate on standing.
Is a colloid the same thing as a dispersion?
A colloid is one specific type of dispersion, one whose particles fall in the roughly 1 to 1000 nanometer size range, large enough to scatter light via the Tyndall effect but too small to settle out under normal gravity.