WATER SOLUTIONS
To make molecules or ions of another substance go into solution, water molecules
must overcome the forces that hold these molecules or ions together. The
mechanism of the actual process is complex. To make sugar molecules go into
solution, the water molecules cluster around the sugar molecules, pull them off,
and disperse, forming the solution.
For an ionic crystal such as salt, the water molecules orient themselves
around the ions (which are charged particles) and again must overcome the forces
holding the ions together. Since the water molecule is polar, this orientation
around the ion is an attraction of the polar ends of the water molecule. For
example:
Once surrounded, the ion is insulated to an extent from other ions in solution
because of the dipole property of water. The water molecules that surround the
ion differ in number for various ions, and the whole group is called a hydrated
ion.
In general, as stated in the preceding section, polar substances and ions
dissolve in polar solvents and nonpolar substances such as fats dissolve in
nonpolar solvents such as gasoline. The process of going into solution is
exothermic if energy is released in the process, and endothermic if energy from
the water is used up to a greater extent than energy is released in freeing the
particle.
When two liquids are mixed and they dissolve in each other, they are said to
be completely miscible. If they separate and do not mix, they are said to be
immiscible.
Two molten metals may be mixed and allowed to cool. This gives a “solid
solution” called an alloy.
CONTINUUM OF WATER MIXTURES
Figure 32 shows the general sizes of the particles found in a water mixture.