Colloids

When salt is added to water, it dissolves to form a solution. Conversely, when sand is added to water and stirred, the sand particles are spread throughout the liquid to form a suspension, and finally settle at the bottom.

However, when flour is added to water, the water becomes cloudy. This is because flour and water form a colloidal dispersion or a colloid.

A colloid is a mixture in which particles of a solute-like substance are finely dispersed in a solvent-like medium.

The dispersed particles and the dispersing medium can be any combination of solid and liquid, such as opal, liquid and liquid, such as milk, liquid and gas, such as whipped cream, except that they cannot both be gases.

Properties of a colloid are intermediate between those of suspensions and solutions.

Colloids are heterogeneous mixtures like suspensions, in contrast to solutions, which are homogeneous.

With a size of 5 to 1000 nanometers, colloidal particles are much larger than the usual solute molecules, which are around 1 nanometer or less, and smaller than suspended particles, which are 10,000 nanometers or larger.

A laser beam passing through a solution is invisible but can be easily seen in a colloidal dis