Chapter 60

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.