110 THE THEORY OF IONIZATIONNeither the acid nor the base alone furnishes many ions, but
when they are mixed, the H+ and OH" ions present unite at once.
This leaves the un-ionized parts of the acid and base out of equi-
librium, and further ionization occurs in consequence. This
process continues until both the acid and the base have become
fully ionized because there can be no accumulation of H+ and OH"
ions in presence of each other.
The neutralization of a weak acid and a weak base then con-
sists of three simultaneous but distinct ionic reactions: the ion-
ization of the acid, the ionization of the base, and the formation
of water from its ions. These reactions may be arranged in an
intersecting form in order to show which of the components take
part simultaneously in two reactions:
HC2HA ^ H+ + C2HA"
NH4OH ^ OH" + NH 4 +
H 2 O
As this train of reactions proceeds it is obvious that NH.4+ and
C2H3O2" ions, that is, the ions of the salt ammonium acetate, ac-
cumulate in the solution, and that their presence accounts for the
high conductivity of the neutral solution.
The total heat effect, 12,000 calories, produced by the action of
one equivalent of acetic acid and one equivalent of ammonium
hydroxide, is the sum of the heat effects of the three separate reac-
tions, and we should expect the value to be different from the
value of the neutralization of a strong acid and a strong base.
Since 13,700 calories must be generated by the formation of 1
mole of water, the difference between this value and 12,000, or 1,700
calories, must have been absorbed in the ionizing of the acid and
the base.
Displacement of a Weak Acid from Its Salt. When a salt of a
weak acid is treated with the solution of a strong acid the ions
of the weak acid unite to form un-ionized molecules and the salt
of the strong acid remains. One example of such a displacement
has been seen (p. 88, Exp. 10 (&)) in the action of sulphuric acid
with sodium acetate
2H+ SO 4 ""
2C 2 H 3 O 2 " 2Na+
jr
2HC2H3O2