Ammonia, << uh MOHN yuh or uh MOH nee uh, >> is a colorless gas made up of one part nitrogen and three parts hydrogen. It is lighter than air and has a sharp, stinging odor. Ammonia can be inhaled safely if it is greatly diluted in air, but concentrated ammonia gas can cause suffocation and death. Ammonia does not burn in air, but it burns in oxygen with a weak yellow flame. Chemists classify ammonia as a base.
Properties of ammonia.
Ammonia is highly soluble in water and forms a solution known as ammonium hydroxide (ammonia water). Ammonia is not very reactive when dry, but it reacts with many chemicals when dissolved in water. Ammonium hydroxide neutralizes acids and forms the corresponding ammonium salts. For example, hydrochloric acid added to ammonium hydroxide produces a solution of ammonium chloride. When combined with some metals, ammonium hydroxide forms complex compounds called ammines. For example, the addition of ammonium hydroxide to a pale blue solution of cupric sulfate produces a deep blue solution of cupric ammine sulfate.
Ammonia gas changes to a liquid at –33.35 °C. Liquid ammonia boils at the same temperature. It freezes to a clear solid at –77.7 °C. In going from a liquid back to a gas, ammonia absorbs a large amount of heat from its surroundings. Upon evaporation, one gram of ammonia absorbs 327 calories of heat. For this reason, ammonia is widely used in refrigeration equipment.
Preparing ammonia.
In the laboratory, ammonia is prepared by heating an ammonium salt with sodium hydroxide. The ammonia gas given off can be identified by its odor and by its ability to turn moist litmus paper from red to blue.
Commercially, ammonia is made by the Haber process, which combines free nitrogen and hydrogen gases, both of which can be obtained easily and cheaply (see Haber process ). One volume of nitrogen is mixed with three volumes of hydrogen under high pressure and temperature in the presence of an iron catalyst (see Catalysis ). Ammonia is also obtained as a by-product in the production of coal and coke gas.
Uses.
Ammonia is widely used as a fertilizer. Ammonium nitrate and other ammonium salts help to increase crop production because they have a high percentage of nitrogen. In some farming areas, anhydrous ammonia is now applied directly to the fields from large tanks that contain the compressed gas.
Large quantities of ammonia are oxidized to make nitric acid, which is needed to make such explosives as TNT (trinitrotoluene), nitroglycerin, and ammonium nitrate. The textile industry uses ammonia in the production of synthetic fibers such as nylon and cuprammonium rayon. Ammonia is also used in dyeing and scouring cotton, wool, and other fibers. Ammonia water sometimes serves as a cleaning fluid and can be used to restore fabrics that have been stained by acids.
Ammonia is also vital in the manufacture of many chemicals, plastics, vitamins, and drugs. For example, it acts as a catalyst in making plastics such as Bakelite, and it is used as a reactant in making melamine resins for plastics.
