http://www.ck12.org Chapter 15. Water
Introduction
In the previous lesson, we studied how aqueous solutions are formed. Our focus was on solid or liquid solutes being
dissolved by liquid water, and we assumed that the solutes were either completely soluble or completely insoluble,
producing either homogeneous or heterogenous mixtures, respectively. However, there are other situations that are
not as easy to classify. For example, inFigure15.14, we see a small bowl of mayonnaise. Mayonnaise is a colloid
–a mixture that is not totally homogeneous nor totally heterogeneous. In this lesson, we are going to expand our
study of mixtures to show that solids and gases can also act as solvents. Additionally, we will look at situations in
which a solute breaks down into particles that are larger than individual molecules and ions but smaller than, say, a
fully intact grain of sand.
FIGURE 15.14
Colloids and Suspensions
Solutions are comprised of a solvent and a solute, mixed homogeneously to produce a transparent fluid. However,
there are also mixtures in which the solute is evenly dispersed, but each solute particle is still a cluster of more
fundamental particles like molecules or ions. The particle sizes in such mixtures are generally larger than 1× 10 −^9
meters. Such a mixture cannot easily be classified as either homogeneous or heterogeneous. In such systems, we
often use the termsdispersed phaseandcontinuous phase(ordispersion medium) in place of solute and solvent.
Each of these phases can consist of a solid, liquid, or gas.Table15.3 shows various combinations of dispersed and
continuous phases.