What are solutions, colloids, and suspensions?

Question

Luna Chen · Accepted Answer

These are three types of mixtures that are distinguished by the sie of the particles being mixed, and other properties (discussed below).

A solution is a mixture of two or more pure substances that is homogeneous, which means that because the mixing happens at the molecular level, it is perfectly uniform everywhere; it will also be transparent and the components will not separate over time or through filtering. In a suspension, larger pieces are matter are combined (most agree on #10^(-5) m# or greater as being the particle size in a suspension. As a result, the mixture will be cloudy or even opaque, and generally separates upon standing. Filtering will generally result in separation is the materials. A true colloid should not separate if left standing. Light passing through a colloid will tend to be scattered, with some light passing through, giving it a translucent appearance. A colloid is sort of "in-between" these two. Particle size is smaller (but not on the molecular level).

Henry Antrim · Answer

Different numbers of phases and stabilities....

Solutions comprise a solute that is solvated by a solvent. Solvation means that the ions in a solution are surrounded by or complexed by molecules of the solvent (its a slightly more complex process for things such as polymer solutions, so I won't go into that here). The fact that the solute ions are completely surrounded by and/or complexed with solvent molecules mean that solutions are single phase and homogenous. In a suspension, however, one phase is simply dispersed into small particles that float around in the solvent. There is no surrounding of, or complexing of, any species at the molecular or ionic level. Suspensions are therefore two phase (either solid/liquid, solid/gas, gas/liquid or liquid/imiscible-liquid) and are heterogeneous. Many suspensions will separate on standing (solid particles fall to the bottom of the container, or gas bubbles coalesce and rise to the top, or two immiscble liquids separate into two layers). Colloids are a specific class of suspensions where the particle size is between 1 and 1000 nanometres (1 x #10^-9# to 1x #10^-6# m). They tend to be much more stable than regular dispersions and do not readily separate on standing. A classic example would be milk.

Wyatt Atkins · Answer

undefined Solutions are homogeneous mixtures composed of a solute dissolved in a solvent. Colloids are heterogeneous mixtures where the dispersed particles are intermediate in size between those of a solution and a suspension. Suspensions are heterogeneous mixtures containing larger particles that settle out over time.