1. Laboratory method. In the laboratory ammonia is prepared from ammonium chloride, a compound having the formula NH4Cl, and obtained in the manufacture of coal gas. As will be shown later in the chapter, the group NH4 in this compound acts as a univalent radical and is known as ammonium. When ammonium chloride is warmed with sodium hydroxide, the ammonium and sodium change places, the reaction being expressed in the following equation.
NH4Cl + NaOH = NaCl + NH4OH.
The ammonium hydroxide (NH4OH) so formed is unstable and breaks down into water and ammonia.
NH4OH = NH3 + H2O.
Calcium hydroxide (Ca(OH)2) is frequently used in place of the more expensive sodium hydroxide, the equations being
2NH4Cl + Ca(OH)2 = CaCl2 + 2NH4OH,
In the preparation, the ammonium chloride and calcium hydroxide are mixed together and placed in a flask arranged as shown in Fig. 35. The mixture is gently warmed, when ammonia is evolved as a gas and is collected by displacement of air.
Fig. 35