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.
Liquid ammonia boils at the same temperature.
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. 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.