The Elements of Qualitative Chemical Analysis, vol. 1, parts 1 and 2.: With Special Consideration of the Application of the Laws of Equilibrium and of the Modern Theories of Solution.Stieglitz, Julius
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The Elements of Qualitative Chemical Analysis, vol. 1, parts 1 and 2.: With Special Consideration of the Application of the Laws of Equilibrium and of the Modern Theories of Solution.
Stieglitz, Julius
Chemistry, Analytic -- Qualitative
There should be no difficulty, therefore, in considering water to
have the chemical properties of a base as well as of an acid. Its
chemical activities as such, weak as they may be, must be satisfied
whenever it is present. These activities lead to the hydrolysis or
the decomposition of salts by water, in greater or lesser degree,
whenever water is used as a solvent for salts.
«Action of Water on a Salt of a Strong Base and a Strong Acid.»—If
sodium chloride, a typical salt formed from a strong base and a
strong acid, is dissolved in water, it is ionized to a considerable
extent. Considering the solution from a mechanical point of view, we
would expect that the sodium ions, moving in all directions, would
collide occasionally with hydroxide ions, which are formed from the
water and are present in minute but definite quantity. Some of the
collisions must result in the formation of sodium hydroxide, as we
have no reason to suppose that the result would differ from that in
other cases where positively charged particles meet with negatively
charged ones. However, since sodium hydroxide is an ionogen, with
a very great tendency to ionize, and since there is present only a
minute concentration of the hydroxide-ion, the [p179] equilibrium
conditions will be satisfied when only traces of the nonionized
hydroxide are formed. In a similar manner, we must expect to have
traces, and only traces, of nondissociated hydrochloric acid formed
by the union of chloride ions with some of the hydrogen ions of the
water. Since hydrogen chloride and sodium hydroxide show practically
the same tendency to ionize (tables, pp. 104 and 106), the two kinds
of ions which water forms, the hydrogen-ion and the hydroxide-ion,
will be used up ‹to a very slight› and practically ‹equal› extent
to form nonionized sodium hydroxide and hydrogen chloride, but the
ions will be immediately regenerated, and in equal concentrations,
from the nonionized water which is present. All the equilibrium
requirements will be satisfied when ‹traces› of sodium chloride
have been converted into nonionized sodium hydroxide and hydrogen
chloride. Such a solution, containing no excess of the hydrogen- or
the hydroxide-ion, would react ‹neutral›. The action may be expressed
by the equation[366]
«NaCl» ⇄ «Na»^{+} + «Cl»^{−}
«H_{2}O» ⇄ HO^{−} + H^{+}
Na^{+} + HO^{−} ⇄ NaOH
Cl^{−} + H^{+} ⇄ HCl.
The decomposition of sodium chloride by water, which one may
predict on the basis of these theoretical considerations, may be
demonstrated, slight as it is, by the following experiment.[367]
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