CHAPTER XXI. SODIUM HYDRATE

101. Preparation.

Experiment 61.--Dissolve 3 g. sodium carbonate, Na2CO3, in 10 or
15 cc. H2O in an e.d., and bring it to the boiling-point. Then
add to this a mixture of 1 or 2 g. calcium hydrate, Ca(OH)2, in 5
or 10cc. H2O. It will not dissolve. Boil the whole for five
minutes. Then pour off the liquid which holds NaOH in solution.
Evaporate if desired. This is the usual mode of preparing NaOH.

The reaction is Na2CO3 + Ca(OH)2 = 2NaOH + CaCO3. The residue is
Ca(OH)2 and CaCO3; the solution contains NaOH, which can be
solidified by evaporating the water. Sodium hydrate is an
ingredient in the manufacture of hard soap, and for this use
thousands of tons are made annually, mostly in Europe. It is an
important laboratory reagent, its use being similar to that of
ammonium hydrate. Exposed to the air, it takes up water and CO2,
forming a mixture of NaOH and Na2CO3. It is one of the strongest
alkalies, and corrodes the skin.

Experiment 62.--Put 20 cc. of H2O in a receiver. With the forceps
take a piece of Na, not larger than half a pea, from the naphtha
in which it is kept, drop it into the H2O, and at once cover the
receiver loosely with paper or cardboard. Watch the action, as
the Na decomposes H2O. HOH + Na = NaOH + H. If the water be hot
the action is so rapid that enough heat is produced to set the H
on fire. That the gas is H can be shown by putting the Na under
the mouth of a small inverted t.t., filled with cold water, in a
water-pan. Na rises to the top, and the t.t. fills with H, which
can be tested. NaOH dissolves in the water.102. Properties.

Experiment 63.--(1) Test with red litmus paper the solutions
obtained in the last two experiments. (2) To 5cc.of alum
solution, K2A12(SO4)4, add 2cc.of the liquid, and notice the
color and form of the ppt.

POTASSIUM HYDRATE.

103. KOH is made in the Same Way as NaOH.

Describe the process in full (Experiment 61), and give the
equation.

Experiment 64.--Drop a small piece of K into a receiver of H2O,
as in Experiment 62. The K must be very small, and the experiment
should not be watched at too close a range. The receiver should
not be covered with glass, but with paper. The H burns, uniting
with O of the air. The purple color is imparted by the burning,
or oxidation of small particles of K. Write the equation for the
combustion of each.

H2O might be considered the symbol of an acid, since it is the
union of H and a negative element; or, if written HOH, it might
be called a base, since it has a positive element and the (OH)
radical. It is neutral to litmus, and on this account might be
called a salt. It is better, however, to call it simply an oxide.

Potassium hydrate, caustic potash, is employed for the
manufacture of soft soap. As a chemical reagent its action is
almost precisely like that of caustic soda, though it is usually
considered a stronger base, as K is a more electro-positive
element than Na.

CALCIUM HYDRATE.

104. Calcium Hydrate, the Most Common of the Bases, is nearly as
important to them as H2SO4 is to acids. Since it is used to make
the other bases, it might be called the strongest base; as H2SO4
is often called the strongest acid. The strength of an acid or
base, however,depends on the substance to which it is applied, as
well as on itself, and for most purposes this one is classified
as a weaker base than the three previously described.

Sulphuric acid, the most useful of the acids, is not made
directly from its salts, but has to be synthesized. Calcium
hydrate is also made by an indirect process, as follows:

CaCO3, i.e. limestone, marble, etc., is burnt in kilns with C, a
process which separates the gas, CO2, according to the reaction:
CaCO3 = CaO + CO2. CaO is unslaked lime, or quick-lime. On
treating this with water, slaked lime, Ca(OH)2 is formed, with
generation of great heat. CaO + H2O = Ca(OH)2. Its affinity for
H2O is so great that it takes the latter from the air, if
exposed.

Experiment 65.--Saturate some unslaked lime with water, in an
e.d., and look for the results stated above, leaving it as long
as may be necessary.

105. Resume.--From the experiments in the last few chapters on
the three divisions of chemical compounds, acids, bases and
salts, we have seen (1) that acids and bases are the chemical
opposites of each other; (2) that salts are formed by the union
of acids and bases; (3) that some acids can be obtained from
their salts by the action of a stronger acid; (4) that some bases
can be got from salts by the similar action of other bases; (5)
that the strongest acids and bases, as well as others, may be
obtained in an indirect way by synthesis.