l^{-} + H_{2}O + 13,700 cal.

K^{+}, OH^{-} + H^{+}, NO_{3}^{-}
= K^{+}, NO_{3}^{-} + H_{2}O + 13,700 cal.

Ca^{++}, (OH)_{2}^{--} + H_{2}^{++}, SO_{4}^{--}
= Ca^{++}, SO_{4}^{--} + 2H_{2}O + 2 x 13,700 cal.

~Neutralization a quantitative act.~ Since neutralization is a definite
chemical act, each acid will require a perfectly definite weight of each
base for its neutralization. For example, a given weight of sulphuric
acid will always require a definite weight of sodium hydroxide, in
accordance with the equation

H_{2}, SO_{4} + 2Na, OH = Na_{2}, SO_{4} + 2H_{2}O.

~Determination of the ratio in neutralization.~ The quantities of
acid and base required in neutralization may be determined in
the following way. Dilute solutions of the two substances are
prepared, the sulphuric acid being placed in one of the
burettes (Fig. 34) and the sodium hydroxide in the other. The
levels of the two liquids are then brought to the zero marks of
the burettes by means of the stopcocks. A measured volume of
the acid is drawn off into a beaker, a few drops of litmus
solution added, and the sodium hydroxide is run in drop by drop
until the red litmus just turns blue. The volume of the sodium
hydroxide consumed is then noted. If the concentrations of the
two solutions are known, it is easy to calculate what weight of
sodium hydroxide is required to neutralize a given weight of
sulphuric acid. By evaporating the neutralized solution to
dryness, the weight of the sodium sulphate formed can be
determined directly. Experiment shows that the weights are
always in accordance with the equation in the preceding
paragraph.

[Illustration: Fig. 34]

~Extent of dissociation.~ The question will naturally arise, When an acid,
base, or salt dissolves in water, do all the molecules dissociate into
ions, or only a part of them? The experiments by which this question can
be answered cannot be described here. It has been found, however, that
only a fraction of the molecules dissociate. The percentage which will
dissociate in a given case depends upon several conditions, the chief of
which are: (1) The concentration of the solution. In concentrated
solutions only a very small percentage of dissociation occurs. As the
solution is diluted the percentage increases, and in very dilute
solutions it may be very large, though it is never