How does a solution differ from a colloid?

Question

Avery Adams · Accepted Answer

Colloids contain two distinct phases separated by an interface. Solutions contain one distinct phase, and no interface.

Take a typical colloid, e.g. pigmented ink. The tiny particles of pigment are uniformly distributed throughout the carrier liquid, but if you look at it under a microscope you can see the many tiny little particles of pigment, with a clear interface between the pigment and the liquid (it is the surface of the little particles). Now take a solution, like salt water. Look at this under a microcope and you see....nothing. The reason is that solutions are single phase, where the solute is effectively broken up into component ions and solvated by the solvent molecules. No physical "interface" exists.

Avery Adams · Answer

undefined A solution is a homogeneous mixture of two or more substances, where the solute is dissolved in the solvent. A colloid, on the other hand, is a heterogeneous mixture where the dispersed particles are larger than individual molecules but smaller than those in a suspension. The particles in a solution are smaller and do not scatter light, while the particles in a colloid are larger and can scatter light, causing the mixture to appear cloudy.