CHAPTER IIWATER AND SOLUTIONWater is in many respects the most important and interesting
substance on the earth's surface. By its presence in abundance
the physical and chemical conditions necessary for the existence
of life are maintained on the earth. By far the greater part
of the chemical changes, both in nature and in industry, which have
a direct bearing on human life and welfare, involve water, either as
a direct participant in the change or as a solvent for the substances
which are changing.
PREPARATION 1
POTASSIUM NITRATE, KNO 3 , FROM SODIUM NITRATE AND
POTASSIUM CHLORIDE
Solubility plays a controlling part in many chemical processes
of which the present one is a typical example.
Salts, as well as strong acids and strong bases, exist in a pe-
culiar state when they are in solution. This is known as the state
of ionization and is more fully dealt with in Chapter III; but for
our present purposes it is sufficient to know that salts consist of
electrically charged radicals, the metallic radicals being positive
and the non-metallic radicals negative. These radicals are held
together in the compound by electrostatic attraction, which is
enormous. When the salt is in solution, the electrostatic at-
traction still exists and prevents the negative radicals from getting
away from the positive radicals, but there is a certain freedom
of movement which allows radicals to exchange places easily,
subject only to the condition that every negative radical must be
electrically balanced at all times by some positive radical.
When sodium nitrate and potassium chloride are dissolved,
the solution contains four ions, Na+, NO3", K+, CP, and from
these ions not only could the two original salts be reconstructed,
but also two new salts, potassium nitrate and sodium chloride,
through a regrouping of the radicals. Which of the four salts will
crystallize from a solution containing the four ions depends solely
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