particle is usually in the range of from 1 to 200 nanometers (nm) in diameter. This
range has been arbitrarily set since particles with a diameter of less than 1 nm do not
scatter light and particles greater than 200 nm can be seen with the light microscope.
As was mentioned above, there is no homogeneity of particles in this type of solution.
The particles are actually suspended in the solvent. A colloidal solution is broken down
into two parts: (1) the dispersed phase (analogous to the solute of a true solution) and
(2) the dispersion medium (analogous to the solvent of a true solution). The most
important colloidal systems are those involving a solid dispersed in a liquid and are
commonly denoted as colloidal suspensions. In some determinations of amylase, the
starch substrate is a colloidal suspension.
Emulsions are colloidal solutions in which the dispersed phase and the
dispersion medium are immiscible. If one mixes water and oil together and then shakes
the container, the oil will break into very small particles that will disperse within the
water. Upon standing, the oil droplets (dispersed phase) will tend to coalesce, forming
larger and larger droplets. These droplets eventually become too large to remain within
the dispersion medium (water) and the two liquids will separate. If one wishes to
stabilize an emulsion, an emulsifying agent such as a bile salt must be added.
2-24. SATURATED SOLUTIONS
The laboratory specialist may on occasion be required to prepare a saturated
solution. This type of solution is defined as a solution in which the dissolved solute is in
equilibrium with undissolved solute. At a given temperature, most solutions can
dissolve (hold) only a given number of solute particles. Once this solution contains all
the solute particles that it can "hold," any additional solute will settle to the bottom of
the container. Once this point has been reached, the solution is said to be saturated.
As stated, there is an equilibrium between dissolved and undissolved solute. More
clearly, this is to say that dissolved solute is continuously leaving the solution and
entering into the crystal lattice of the undissolved solute. At the same time, undissolved
solute is leaving the crystalline state and entering into solution.
2-25. UNSATURATED SOLUTIONS
An unsaturated solution is one that does not contain all the solute molecules that
the solution could possibly "hold."
Section V. PERCENT CONCENTRATION
The simplest solution to prepare in the laboratory is the percent solution. The
main reason that this type of solution is commonly used is the ease in calculating the
amount of solute needed in its preparation. The term percent is a shortened form of