An Elementary Study of Chemistry

by William McPherson; William Edwards Henderson

Fig. 36

Ammonium hydroxide (NH₄OH). The solution of ammonia in water is found to have strong basic properties and therefore contains hydroxyl ions. It turns red litmus blue; it has a soapy feel; it neutralizes acids, forming salts with them. It seems probable, therefore, that when ammonia dissolves in water it combines chemically with it according to the equation

NH₃ + H₂O = NH₄OH,

and that it is the substance NH₄OH, called ammonium hydroxide, which has the basic properties, dissociating into the ions NH₄ and OH. Ammonium hydroxide has never been obtained in a pure state. At every attempt to isolate it the substance breaks up into water and ammonia,—

NH₄OH = NH₃ + H₂O.

The ammonium radical. The radical NH₄ plays the part of a metal in many chemical reactions and is called ammonium. The ending -ium is given to the name to indicate the metallic properties of the substance, since the names of the metals in general have that ending. The salts formed by the action of the base ammonium hydroxide on acids are called ammonium salts. Thus, with hydrochloric acid, ammonium chloride is formed in accordance with the equation

NH₄OH + HCl = NH₄Cl + H₂O.

Similarly, with nitric acid, ammonium nitrate (NH₄NO₃) is formed, and with sulphuric acid, ammonium sulphate ((NH₄)₂S0₄).

It will be noticed that in the neutralization of ammonium hydroxide by acids the group NH₄ replaces one hydrogen atom of the acid, just as sodium does. The group therefore acts as a univalent metal.

Combination of nitrogen with hydrogen by volume. Under suitable conditions ammonia can be decomposed into nitrogen and hydrogen by passing electric sparks through the gas. Accurate measurement has shown that when ammonia is decomposed, two volumes of the gas yield one volume of nitrogen and three volumes of hydrogen. Consequently, if the two elements were to combine directly, one volume of nitrogen would combine with three volumes of hydrogen to form two volumes of ammonia. Here, as in the formation of steam from hydrogen and oxygen, small whole numbers serve to indicate the relation between the volumes of combining gases and that of the gaseous product.