The hydrogen bond is a very weak attraction about 1/10 to 1/20 the strength of the
hydrogen-oxygen covalent bond. The hydrogen bond explains why water has such a
high boiling point in relation to other compounds of similar molecular weight. For
example, methane (CH4, molecular weight = 16) boils at a temperature below 0C, while
water (molecular weight = 18) boils at 100C. Methane does not exhibit hydrogen
e. Water Purification. We are all familiar with some of the ecological problems
we will often be using water in the preparation of our products, we must be concerned
with its purity and the methods utilized for its purification. There are two common
methods of water purification used at Army medical treatment facilities--distillation and
(1) Distillation. Distillation is the process of boiling water, collecting the
vapor, and then condensing the vapor back into water. Minerals and some of the
bacterial contamination will remain in the boiling vessel as a residue. Very pure water
may be prepared by repeating the distillation process several times. If sterile water is
desired, the water must be sterilized, because the process of distillation does not
necessarily sterilize water.
(2) Ion exchange (deionization). Less common than distillation because it is
less efficient, ion exchange involves passing water through a column containing a
charged resin. Ions in the water are held by electrical attraction and are thus removed
from the water.
We are seldom concerned with just water in the hospital. We are generally more
concerned with substances dissolved in water. These are solutions. When we speak of
a solution, there are several terms, which are important to understand.
a. Solute. A solute is the substance, which is dissolved in a solution.
b. Solvent. The solvent is, the substance, which dissolves the solute. It is
usually water in pharmaceutical solutions, but not always.
c. Solubility. The maximum amount of a compound, which will dissolve in a
given amount of solvent at a given temperature is the solubility of that compound.
d. Dissociation. (Ionization). In general, two things can happen to a solute in a
solution. It can dissolve and exist in solution as molecules or it can dissociate and exist
entirely or partially as ions. The process of splitting a molecule into ions is known as