15.3. Colloids and Suspensions http://www.ck12.org
TABLE15.3: Dispersed Phase
Gas Liquid Solid
Continuous Gas Phase nonegases are miscible liquid aerosolfog, mist solid aerosolsmoke
Continuous Liquid Phase foamwhipped cream emulsionsalad dressing suspension or sol paint,
ink
Continuous Solid Phase solid foamstyrofoam geljelly solid solglassA mixture of two gases will always be homogeneous. It can be referred to as a solution, but it is often simply called
a gas mixture. When a gaseous solute is dispersed within a liquid phase (e.g., whipped cream) or a solid phase (e.g.,
styrofoam), the result is generally referred to as a foam. A mixture in which liquid particles are dispersed in a gas
are called aerosols; examples include fog or hair spray. Liquid particles dispersed into a liquid (e.g., mayonnaise) or
solid (e.g., jelly) are called emulsions and gels, respectively. A solid dispersed into a gas, such as smoke, is referred
to as a solid aerosol. Solid particles dispersed into liquids (e.g., paint) or solids (e.g., opaque glass) are called sols
and solid sols, respectively.
We can further differentiate between different mixtures by looking at the particle size of the dispersed substance (
Figure15.15).
FIGURE 15.15
Particle Size and Solution TypeTrue solutions generally have particle sizes that are smaller than one nanometer. The particles in these solutions
do not settle over time and cannot be separated by filters or semi-permeable membranes. The dispersed particles
incolloidsusually range in size from 10−^9 to 10−^7 meters. These solutions are somewhat transparent, and their
particles do not settle out over time. However, with fine enough semi-permeable membranes, the dispersed particles
in a colloid can be separated from the bulk solvent. Suspensionshave the largest particles sizes, on the order of
10 −^7 meters or larger. These mixtures are opaque, and the particles can be separated by filtration. Additionally, the
particles in a suspension separate over time into different layers based on the relative densities of the dispersed and
continuous phases.
Visible Effects of Particle Size
On the macroscopic scale, variations in particle size can be detected by the effect they have on light that passes
through the mixture. For example, true solutions are transparent. Some solutions are colored, which means
that certain wavelengths of light are absorbed by molecules within the mixture. However, the remaining light is
transmitted freely through the mixture. In contrast, the dispersed particles in a colloid scatter light, resulting in an
opaque mixture. The difference can be seen inFigure15.16. The phenomenon in which light is scattered by very
small particles in its path is known as theTyndall effect.